The History Of Greek and Roman Technology - Part 1

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your lecture is dr stephen ressler dr ressler is  professor emeritus at the united states military   academy at west point where he taught for 21 years  he holds ms and phd degrees in civil engineering   from lehigh university he is the creator of the  west point bridge design contest a nationwide   competition that introduces engineering to middle  and high school students among numerous other   prestigious awards dr ressler has received the  president's medal and outstanding projects and   leaders award from the american society of civil  engineers and the bliss medal for outstanding   contributions to engineering education from  the society of american military engineers welcome to this course on the  technology of ancient greece and rome when you consider these great civilizations of  classical antiquity what's the first thought   that comes to mind if you're culturally minded  perhaps it's a particular piece of greek sculpture   tragedy by sophocles or one of plato's dialogues  perhaps homer's iliad or virgil's aeneid   if you're into politics maybe it's athenian  democracy or the roman republic if you like sports   you're probably thinking of the olympic games or  bloody gladiatorial contests in the roman arena   military history buff no doubt you're imagining a  great battle like marathon thermopylae or actium   well i'm an engineer so when i  think about classical antiquity   i think about technology monumental  structures like the parthenon and   the coliseum infrastructure systems like vast  roman water supply networks and surprisingly   sophisticated machines like water powered  mills construction cranes and catapults   my overarching goal for this course is  to share this latter perspective with you   to augment your appreciation for the cultural  political and historical dimensions of classical   antiquity by providing you with an opportunity  to explore its technological dimension as well   from an engineering perspective when all is  said and done i hope you'll have learned to   see these great civilizations in a broader richer  and more satisfying way to illustrate this point   let's consider one of the most pivotal events  in human history the battle of salamis which   occurred in september of 480 bc now the narrative  of this great naval confrontation between greeks   and persians is quite familiar particularly  to those of us who've partaken of the great   course's many offerings in ancient greek history  but to briefly summarize king xerxes of persia   had invaded greece with an immense multinational  army and a supporting fleet of over 1 000 warships   on land xerxes army crushed the greek's four  defense at thermopoli pass and then marched   south to sack athens and seized all of attica  except salmos island but at salamis a small greek   fleet opposed the persians at sea and won an epic  victory that changed the course of world history the warships on both sides of this battle  were triremes 125 foot long wooden galleys   each rowed by 170 men arrayed on three levels the  trireme was in essence a human-powered torpedo   it engaged enemy vessels by ramming them with a  bronze clad ram on its prow and engaged they did   having lured the mighty persian armada into the  narrow straits separating salamis island from   the mainland the greeks won a stunning victory  despite being outnumbered three to one the battle   of salamis cost the persians some 300 ships and  tens of thousands of crewmen it dealt a death blow   to the persian invasion and it opened the door  to the extraordinary cultural achievements of   classical greece on that fateful day in 480 bc the  philosophy of socrates the history of herodotus   and the elegant buildings on the acropolis  all were yet to come all would emerge from   a flourishing athenian democracy over the next  century and would ultimately become integral to   our very definition of western culture in a real  sense then the battle of salamis changed the world   so why did the greeks win at salamis well  certainly they employed a superior strategy   choosing to fight in the narrow channel where the  persian's advantage in numbers would be negated   surely the greek cultural predisposition toward   metis or cunning was also a factor as the athenian  general the mystically is used a brilliant   ruse to lure the persians into the channel the  night before the battle politics influenced   the outcome as well most of the persian fleet was  manned by conquered peoples phoenicians egyptians   carrions ionian greeks all fighting to fulfill  their obligation to xerxes their imperial master   the historian herodotus tells us that the captains  of the persian fleet repeatedly made poor tactical   decisions because they were preoccupied with  impressing the great king and their rank and file   oarsmen subjects of a despotic ruler could hardly  have rode with the same do-or-die spirit as the   greeks free citizens whose families and cherished  homeland hung in the balance no doubt then   strategic cultural and political factors  contributed to the greek victory at salamis but   there's also an important technological dimension  to this story and i suggest that we can't fully   understand the historical event without also  understanding how is influenced by technology but how could technology have mattered  at salamis when both sides were using   the same type of warship the trireme well the  answer to that question is that the greeks and   persians employed this technological  system quite differently at salamis   consider for example that during the night before  the battle the entire greek fleet had been dragged   up onto the northern shore of salamis island while  the persian fleet spent the night at sea arrayed   in full battle order with crews manning their oars  why the difference well the greeks were following   standard practice for the employment of triremes  which were typically pulled onto shore every night   so their wooden hulls could be dried out and  protected from the teredo worm a particularly   destructive type of wood boring mollusk native to  the mediterranean region this practice was unique   to warships merchant vessel halls of this era  were covered with a thin layer of lead sheeting   so they didn't have to be dragged onto shore for  protection but lead sheeting couldn't possibly   have been used on a trireme because it would have  made the ship unacceptably heavy as we'll learn   in lecture 23 the trireme was probably the most  optimized mechanical system in all of antiquity   because it was employed as a human-powered torpedo  it had to be fast and maneuverable thus the hull   had to be as light as possible yet strong enough  to withstand the extreme structural demands of   ramming enemy ships in a battle like salamis  even a small engine performance might be the   difference between life and death victory and  defeat so the practice of hauling those ships   onto shore at night was really just a price  that had to be paid for optimal performance   but then why did the persian ships remain at  sea for the entire night before the battle   well xerxes ordered them to sail into the channel  and to remain at the ready to prevent the greeks   from escaping but this action proved to be  unnecessary because the greeks weren't trying   to escape and ill conceived because it ignored  two key technological limitations of the trireme   first without having been dried out on shore  the persian hulls would have been waterlogged   and therefore slower than their greek adversaries  and more importantly the persian oarsmen the human   engines of the trireme would have rode into battle  without having slept for a full 24 hours prior   now for the sake of optimized performance the  trireme was built just barely large enough to   accommodate its 170 rowers seated on their wooden  benches packed into the hull like sardines in a   can these men couldn't possibly have slept or  prepared meals at sea it's also worth noting   that a healthy adult can produce sustained power  output of about one-tenth horsepower more or   less indefinitely but a well-rested man in good  physical condition can produce over one horsepower   for short periods given this 10-fold range in  potential human power output the persian crew's   fatigue would have resulted in a substantial  degradation of their ship's performance   furthermore herodotus tells us that xerxes  augmented each trireme standard crew with   30 persian soldiers probably to ensure that those  phoenician egyptian and ionian oarsmen remained   loyal to the great king but these additional  troops would have increased the overall weight   of each ship by about eight percent and because  these men could only have been stationed on   its upper deck they would have made the vessel  dangerously top-heavy this situation would have   been greatly exacerbated by the fact that triremes  carried no ballast that extra weight that merchant   ships of this era placed deep in their holds to  enhance the resistance to capsizing but would   have been unacceptably heavy and therefore would  have unacceptably impeded a trireme's performance   there can be no doubt then that the greek  victory against such incredible odds at   salamis can be attributed at least in part to the  combined effects of the persian ship's overloaded   unstable waterlogged hulls and the reduced  power output of tired hungry oarsmen   these factors are all associated in  some way with the unique technological   characteristics of the trireme how could we  really understand what happened at salamis   without first understanding the capabilities and  limitations of this fascinating engineered system so why is ancient technology worth learning  about well i'll suggest three reasons   first as we saw at salamis technology can  sometimes influence the course of human   events quite directly but even when it doesn't  technology always reflects the social political   and cultural context from which it emerged thus we  can appreciate an ancient civilization more deeply   if we understand something about the  technological developments it fostered   second we should know about greek and roman  technologies because they've influenced our own   modern world in so many substantive ways now  the modern legacy of ancient technology will   be the principal focus of our final lecture in  this course so i won't go into it in detail here   but i do think you'll be amazed at the  extent to which we all encounter this legacy   in our daily lives my third and most heartfelt  reason for studying greek and roman technology is   that this technology is just so darn interesting  sometimes even astonishing this is particularly   true because the design of ancient technologies  was severely constrained by relatively crude   materials extremely limited sources of power  and lack of scientific models that could be   used to predict the behavior of physical systems  as scientific models are used in engineering today   as a result ancient engineers had to be  exceptionally clever in designing structures and   mechanical devices and these systems often display  the ingenuity of their creators with great clarity   learning to discern and appreciate this virtuosity  and design is for me the greatest source of joy in   studying ancient technology now to reinforce  this point let's look at a particularly   fascinating piece of ancient machinery a greek  stone-throwing catapult called the palintone   we'll examine this machine in great detail  during lecture 21 so for now i only want to wet   your appetite developed during the 4th century bc  the palintone was the product of a developmental   process that began with a conventional bow and  arrow and culminated in a machine that looked   just like this but was 20 times larger now the  palatone is classified as a torsion catapult   and that refers to the fact that its principle  source of power is these two torsion springs so   what's torsion well the word torsion refers to  the twisting typically of a structural element   and that's indeed precisely how these springs  operate my model uses nylon rope for the torsion   springs which is actually a very poor substitute  for the actual material used in the greek palatone   animal tendons or sinew and if the use of  animal tendons to power a catapult seems odd   well it's a fact that the greeks couldn't  have chosen a better material for the job   it turns out that the effectiveness of a  spring depends on its ability to store elastic   energy and sinew has 20 times the capacity for  elastic energy storage of modern structural steel   these sinew ropes were then wound into bundles  supported on this wooden end metal framework   and then wooden throwing arms were thrust  into the bundles as you can see here a sling was then stretched between the ends  of those throwing arms and then that sling was   engaged in a rather ingenious trigger device once  the trigger was engaged a projectile was placed   behind the sling and in an actual palatone  that projectile might very well be a stone   ball weighing as much as 200 pounds in order to  [ __ ] the weapon two operators would have used   these hand spikes inserted into the device  here at the rear of the machine called a   windlass and by the way the windlass is believed  to have been invented by no less than archimedes   that great greek mathematician who we'll be  talking about quite often during this course the   two operators turn the windlass by pulling their  hand spikes back one quarter of turn at a time   and through the ingenious configuration of this  device they're able to provide a continuous pull   by alternating the use of the two hand spikes  now as i'm rotating the windlass if you look   forward on the front end of the palatone  you'll notice that as the windlast pulls back   this wooden tray called the slider which also  includes the trigger mechanism and now the sling the rear motion of the slider is rotating  the throwing arms backward as the rope   the throwing arms rotate backwards  they also rotate the torsion springs   and that action the rotation of the springs  is the source of the elastic energy that will   result in the power of the palatone being  ultimately translated into kinetic energy   the energy of motion in this projectile  so once the device has been fully cocked like this notice that this ratchet  mechanism on the side clicks into place   and allows the slider to remain in position even  though i'm no longer pulling on the windlass   the weapon's now cocked and ready to shoot all  i need to do in order to fire it is to swing it   around on its support take aim at some barbarian  target off in the distance and pull the trigger wait a minute you know before i shoot this thing  we really should spend some time talking about the   historical development of the palatone and  also discussing the engineering principles   that govern its operation so we'll return to  the palatone in lecture 21. remember i did   say i was only going to wet your appetite now  at this point if you're convinced that ancient   technology is worth studying we should spend a few  minutes talking about how we're going to study it   the scope of this course is limited primarily to  the development of large-scale engineered systems   during the period of classical antiquity though  we will occasionally look at earlier technologies   when they're relevant to the subject at hand the  term classical antiquity refers to greco-roman   civilization during a 1300 year period that spans  five major historical errors the greek archaic   era which began around 800 bc when homer's  epic poems were first being written down   the hellenic era also called the era of classical  greece which began with the emergence of athenian   democracy around 500 bc and ended with  the death of alexander the great in 323 bc   the hellenistic era characterized by the spread of  greek influence through much of the mediterranean   world under the auspices of competing  kingdoms established by alexander's successors   the roman republic which was established in  509 bc and initially coexisted with those   hellenistic kingdoms but ultimately conquered  them all and finally the roman imperial era   which is generally dated from 27 bc  when octavian assumed the title augustus   to 476 a.d when the last western roman emperor  was deposed although our course spans this 1300   year period its organization is thematic rather  than chronological these lectures are organized   into three major sections each addressing  a particular category of engineered system   first we'll spend eight lectures examining  important structural and construction technologies   in buildings from the earliest greek temples  to the roman pantheon of the second century a.d   we'll then devote six lectures to greek enrollment  infrastructure systems roads bridges water supply   networks sewage systems and public baths as well  as the urban planning methods that tied all these   systems together and then finally we'll wrap up  the course with eight lectures on ancient machines   used in construction water lifting power  production grain milling and transportation   warning this is not a survey course as  such we won't try to cover every possible   category of ancient technology topics like mining  agriculture time keeping hand tools arms and armor   coinage textiles ceramics glass they're  quite interesting and very important but   they're beyond the scope of this particular  course on large-scale engineered systems   warning this is an engineering course thus in  each technological category we'll be examining   just a few representative examples in depth for  example hundreds of greek temples have survived   from antiquity yet when we consider this topic  in lecture four we'll spend most of our time   exploring just one building the beautiful temple  of concordia at agrigento sicily this is neither   the largest nor the most important dork temple  ever built but it is one of the best preserved and   best documented and so we can use the temple of  concordia as a vehicle for learning deeply about   the greek temple as a technological entity rather  than surveying many examples more superficially   for all the engineering systems we examine  we'll seek to answer three big questions   first how was it built second how did it work  as an engineered system and third how is it   situated within the broader context of  technological development in the ancient world to answer these questions in a rigorous way  i'll be introducing some basic scientific and   engineering principles throughout the course in  our lectures on structures for example we'll learn   some basic concepts in engineering mechanics  how structural elements like beams columns and   arches carry load when we examine infrastructure  systems we'll learn about hydrology hydraulics   and surveying in our study of ancient machines  we'll apply the concepts of energy work power   mechanical advantage and buoyancy don't panic  even if math and science aren't your strong   suit i think you'll find the realm of ancient  technology provides a compelling rewarding and   intensely interesting context for learning some  basic concepts about how our physical world works   as we explore the application of these principles  in an amazing variety of technological systems   we're going to encounter some recurring themes and  i'd like to conclude today's lecture by raising   your awareness of these four threads of continuity  so perhaps they'll be more meaningful to you when   we encounter them later on in the course the first  of these themes took me completely by surprise   when i was preparing the course as i began my  research i fully expected to find a more or less   definitive body of scholarly understandings  about greek and roman technology i was so wrong   in the lectures ahead we'll encounter numerous  cases where the accumulated wisdom of centuries   has only recently been completely overturned  as a result of new archaeological evidence   new analytical tools or new interpretations of old  evidence i'll be doing my best to provide these   recent perspectives throughout the course but  recognize that the story of ancient technological   development is still being written this course  certainly won't be the final word on the subject   we'll see these sorts of scholarly paradigm shifts  in several specific technological categories   like land transport water power and warship design  but this general phenomenon is also evident in a   persistent belief throughout much of the 20th  century that the classical era was actually   a time of technological stagnation this theory  was based primarily on the observation that the   greco-roman world produced very few fundamentally  new inventions and indeed this premise is actually   quite correct inventions that predated the greek  archaic era include animal power metallurgy stone   masonry terracotta the wheel wedge lever pulley  sail and even the arch a technology we normally   associate with ancient rome but is actually much  older but during the entire 1300 year span of   classical antiquity the only major new inventions  were the screw the water wheel and concrete but   does lack of invention really  constitute technological stagnation   many current classical scholars say no they argue  and i agree that proponents of the technological   stagnation theory have defined technological  development far too narrowly as invention and   nothing more a recent more holistic model defines  technological development in terms of four phases   invention the act of implementing  an original idea in a new device   innovation the process by which an invention is  brought into use diffusion the process by which   an innovation is communicated through a social  system and finally technology in use the processes   of employing existing technologies maintaining  them and adapting them to new purposes over time   and by the way if you don't think the employment  of technology is important remember how it   influenced the outcome at the battle of salamis in  terms of this four phase model it's evident that   the greeks and romans did little inventing but  they did contribute immeasurably to technological   development through innovation diffusion and use  for example the greeks didn't invent the lever but   their integration of the lever into the design of  this bronze force pump was a brilliant innovation   note how the rotation of the lever  moves the two pistons in an alternating   up and down cycle that ensures a continuous  flow of pumped water subsequent diffusion of   this device throughout the mediterranean world  resulted in its adaptation to an amazing variety   of applications irrigation water supply mining  fighting removing bilge water from ships and   even spraying perfume during theater performances  we'll be looking at this system in greater detail   when we discuss water lifting devices in lecture  18 and in a broader sense we'll see innumerable   examples of these sorts of creative adaptations  of technology in many of our upcoming lectures   and this brings us to our second major theme that  these ancient engineers were just amazingly clever   people unfortunately we don't know much about them  personally but we can certainly admire their work   the best examples of which reflect  great creativity and design   deep qualitative understanding of engineering  principles and a well-honed ability to translate   their ideas into functioning products any notion  that ancient engineering was primitive can be   summarily dismissed in light of sophisticated  systems like the greek palatone we just examined   third theme the most productive periods  of classical era technological development   occurred under the patronage of powerful political  leaders now in the modern world we have a system   of patent law so that investors inventors can  reap direct economic benefits from their work   but in a world without patents royal patronage  was practically the only way to provide a   similar incentive thus as we'll see technological  development was far more robust in the kingdoms   of the hellenistic world than it had been in  the democratic city-states of hellenic greece   and the engineering achievements of imperial  rome far exceeded those of the roman republic   political patronage of science and technology is  best exemplified by the famed museum of alexandria   established by the ptolemaic kings of egypt around  300 bc and no physical remains of the museum of   alexandria have survived to the present but we  know from ancient texts that this house of the   muses wasn't a museum in the modern sense but  rather a research center that brought together   some of the hellenistic world's finest scholars  to solve practical problems during the coming   lectures we'll meet several of these men tessibius  philo byzantium hero of alexandria and we'll see   the important technologies they developed at this  extraordinary institution our fourth and final   theme is not an observation at all but rather a  person his name is marcus vitruvius polio and he's   the author of day architectura the sole surviving  treatise on architecture and engineering from the   ancient world vitruvius was a first century bc  roman architectus a job title that encompasses not   just architecture but also the modern professions  of engineer construction manager and urban planner   vitruvius is a dominant theme of  this course because day architectura   serves as one of our principal sources for every  major form of classical era technology except   the roman imperial construction methods  that were developed after vitruvius's day   yes we're going to be seeing a lot of this guy  in the lectures ahead now given his role as our   principle source for this course i'd like to  close today's lecture with some thoughts from   day architectura chapter one book one vitruvius's  famous discourse on the qualifications required   of the architectus he must be skillful with the  pencil vitruvius says so he can prepare sketches   and plants he should understand geometry  so he can rightly apply the square and the   level in construction he must know about history  because many architectural features derive from   historical antecedents about philosophy because  it will render him courteous just and honest   about medicine so he can judge water quality law  so he can draw up construction contracts astronomy   so he can design sundials and best of all he must  have an ear for music so he can properly adjust   the tension of catapult springs by plucking  them and discerning the correct musical note well that's quite some job description it sounds  like a typical customer of the great courses   and in the spirit of the great courses  just as vitruvius suggests that the   work of the architectus requires  a learned broadly educated person   so i suggest that studying the work of the  architectus will help us become more learned   broadly educated people as well so study  we shall next lecture our journey begins   with an introduction to engineering materials  the substance of technology until then thank you welcome back in the book of deuteronomy chapter  8 moses tells the hebrews for the lord your god   is bringing you into a good country a land with  springs and fountains welling up in the hills   and valleys a land whose stones contain iron in  whose hills you can mine copper today we're quick   to remember that the promised land was flowing  with milk and honey but to the ancient hebrews   it seemed that iron and copper were at least as  important materials mattered in the ancient world   entire civilizations rose and fell on the  basis of their ability to exploit materials   to enhance their military economic and political  power it's hardly surprising then that the ages of   human history are customarily defined in terms  of their dominant materials the stone age the   bronze age the iron age in that sense the story  of human civilization is the story of materials   just as materials mattered in the ancient world  so they matter in this course to understand say   the parthenon in athens not  just as an architectural wonder   but also as an engineered system we must know  something about the materials used to build it   in today's lecture we'll be considering materials  from two different perspectives first we'll look   at their mechanical properties in a general sense  and then we'll consider six specific materials   stone wood clay copper bronze and iron how  they came into use and how their properties   influenced the design of technological systems  these were the principal materials available to   builders at the dawn of the classical era  so they provide the essential foundation   for understanding the ancient technologies  we'll be discussing throughout this course   let's begin with mechanical properties defined  as characteristics that describe how a material   responds to forces and as you might remember  from your high school physics course a force is   simply a push or a pull defined in terms of both  magnitude and direction in the u.s system of units  

the magnitude of a force is typically measured  in pounds in the metric system we use newtons   so how do forces affect materials when we  say that material like stone or iron has   high strength or low strength what does that  actually mean why are certain materials used   for particular structural applications like  beams or columns for example but not for others   to answer these questions let's go to the  laboratory let's begin with this simple model   of a column it's a structural element that we  might find in a greek temple or a roman basilica here in the laboratory i'm  going to take this column   and i'm going to place it  inside this testing frame then we're going to load the testing frame  with bricks representing the portion of the   structure above the column the port portion of the  structure that's actually supported by the column   and if you look very closely you'll notice that  as i add bricks to the column it is compressing   it's getting shorter it's deforming its length  is decreasing and of course this particular model   column is made of styrofoam but it's important  to recognize that a stone column behaves in   exactly the same way it would get shorter  under the equivalent loading of course the   amount of deformation would be much much less  now as this column shortens it's experiencing   something called stress defined as the intensity  of internal force within a structural element   stress comes in two flavors tension which  is associated with elongation of the element   and compression which is associated  with shortening of the element   the column in our testing frame obviously is  in compression so what physically is stress   when i applied that compressive force to the  column it shortened down at the microscopic level   the individual atoms in the crystal structure were  being pushed ever so slightly closer together but   the bonds between these atoms are quite strong and  they resist being deformed in effect when i push   they push back the effect of these interatomic  bonds resisting deformation is the phenomenon we   call stress mathematically stress is expressed as  force per area for example pounds per square inch   just like pressure the pressure in  your automobile tile tires for example   the area in question is the cross-sectional area  of the element in this case it's the square area   of the column viewed from its ant to illustrate  this concept let's go back to the lab and test a   column made of a material that's a bit closer to  the stone we'll see in so many ancient structures   we study later in this course chalk now this  piece of chalk is about 0.4 inches in diameter and   therefore it's cross-sectional area which we'll  need to determine in order to calculate the stress   is a circular area so we calculate it using the  formula pi r squared in this case that works   out to be 0.126 square inches i'm going to take  that piece of chalk and place it into our testing   machine as a structural column now we're going to  take bricks and load that chalk column we need to   know how much the bricks weigh so as you can see  one brick weighs about four and a half pounds   and so when i take that same brick and place it  in the loading frame it applies a compressive   force to the chalk which therefore experiences  a stress of 4.5 pounds divided by 0.126 square   inches for a stress of 36 pounds per square  inch if i add a second brick the stress doubles   to 72 pounds per square inch now this concept of  stress is extremely important because the most   important mechanical property of a material  its strength is defined in terms of stress   specifically the strength of a material is defined  as the maximum stress the material can withstand   before it breaks before it physically shatters  so how many more bricks do you think i'll need   to add to the loading device before the chalk  crushes in compression now let's give it a try there's three so it failed on the fourth brick four times 4.5  pounds divided by the cross-sectional area of  

the chalk works out to be about 140 pounds  per square inch and so we can conclude that   the strength of that particular piece of chalk in  compression is about 140 pounds per square inch   now this chart summarizes the typical strengths  of the materials we're considering in this lecture   tensile strength compressive strength note that  there's significant variability in these strengths   ranging from over 30 000 pounds per square inch  for iron and bronze to less than 100 pounds per   square inch for clay brick note also that the  tensile and compressive strengths of a given   material are not necessarily the same stone is  much stronger in compression than in tension   my piece of chalk carried 140 pounds per square  inch in compression but in tension it fails at   a much lower stress about 10 psi strength is the  most important mechanical property of a material   but as we'll see other properties also have  influenced ancient technological development   quite significantly these include workability the  extent to which a material can be molded carved or   deformed to attain a desired physical shape and  durability the capacity to resist deterioration   by weathering corrosion or rod we could also  consider fire resistance and aspect of durability   these properties have profoundly influenced  the use of materials through the ages   let's explore this influence by examining the  discovery and early use of these materials from a   broad historical perspective this is a fascinating  story that could easily occupy an entire course   i'll provide just a very brief synopsis here when  our distant ancestors first began manipulating   materials for practical purposes they naturally  used what they found lying about stone and wood   indeed the oldest known man-made artifacts are  simple stone tools really just sharp chips of rock   used for cutting and chopping examples dating  from 2 million years ago have been found in east   africa now by the time our own species homo  sapiens emerged roughly 200 000 years ago   humans were making hand axes more or less like  this one a stone blade bound to a wooden handle   with strips of hide or cemented with tree resin  this is a very early example of combining two   different materials stone and wood each in a  manner consistent with its mechanical properties   stone is quite suitable for the axe head  because when i propel it into the log like this the handle is pushing downward on the ax  head while the wood of the log is pushing   upward and inward stone is extremely strong  in compression and so the fact that it's   being compressed in all directions causes it to  work very effectively in that mode the handle   on the other hand behaves quite differently the  handle is bending under the action of my hand   and the support of the axe head on its opposite  end when it bends it experiences significant   tension on the bottom side compression on the  top side however wood has comparable strengths   in both tension and compression and so it works  quite well for bending note that if the handle   of the hammer were made of stone rather than  wood and we used it in exactly the same mode well it doesn't work quite as effectively why not  because the handle experiences that same tensile   stress as the wooden one did but because stone has  such very low limited tensile strength it breaks   quite readily and makes the tool effectively  useless indeed we still use wooden handles   for hammers and axes and similar hand tools  today a pretty good indicator that prehistoric   tool makers had the right idea the ages the  use of stone and wood advanced considerably   the extent of this advance is evident in the  parthenon of classical era athens with its   elegantly proportioned marble columns and  elaborate wooden roof structure yet hundreds   of millennia after the invention of the primitive  hand axe the parthenon still reflects those same   inherent strengths and limitations of stone  and timber stone is strong in compression so   it's well suited for columns and walls but it's  weak in tension so it's not particularly well   suited for beams which explains why the columns  in the parthenon are spaced so closely together   stone is also quite workable the marble of the  parthenon could be carved with great precision   and it's durable allowing us to enjoy this  architectural marvel 2400 years after it was built   on the other hand timber is reasonably strong in  both tension and compression so it's much better   suited for structural components subjected to  bending like these roof beams wood is easily   cut and joined with simple tools so it was well  suited for this sort of elaborate construction   yet wood lacks durability it's highly vulnerable  to rot and fire so today no greek temple roofs   have survived we can only speculate about their  configuration based on the stone sockets in which   those wooden beams were supported in addition to  stone and wood a third material that was readily   available to prehistoric humans was clay  the distinguishing property of clay is its   workability the ease with which it can be molded  into any shape this property reflects clay's   unique atomic structure consisting of thin layers  of atoms that are only weakly bonded to each other   these layers can slide over each other  easily like playing cards in a deck of cards   making the material very easy to shape now because  of clay's plasticity early builders learned that   they could mold it into bricks these so-called  mud bricks were made by mixing clay with sand and   straw and then packing the material into wooden  molds and placing them in the sun to dry though   mud bricks are easy to produce they make a very  poor structural material sun-dried clay has only   low to moderate compressive strength essentially  zero tensile strength and very poor durability   while ancient builders used mud bricks to  construct many impressive structures ziggurats   temples city walls these structures have mostly  vanished today without near constant maintenance   mudbrick structures tend to disintegrate  over a period of roughly 30 years   of course the poor durability of sun-baked clay  can be overcome by firing it in a kiln when   clay is subjected to intense heat its original  layered atomic structure changes to a more rigid   three-dimensional crystal structure the result  is a ceramic a crystalline material that's   strong heat resistant and water resistant  the technology for producing fired brick is   actually quite ancient at a site in the modern  czech republic archaeologists have found small   fired clay figurines from 26 000 years ago the  technology took a long time to take hold though   by the 7th millennium bc useful artifacts like  pots and jars were being made from kiln-fired clay   by the way despite the clear superiority of  fired clay unfired mud brick construction is   still quite common today in regions of the world  that don't have enough timber to fuel their kilns   places like afghanistan where i  spent some time a few years ago   now from our moderate vantage point the discovery  of fired clay might not seem terribly significant   but it truly was a monumental event in the  development of civilization before that discovery   humans were only able to change the shape of a  material say by carving stone or cutting wood   clay was the first material that humans were able  to transform into a fundamentally new substance   thus fired clay was in effect the first true  man-made material the immediate uses of fired   clay or terracotta were revolutionary in their  own right durable bricks and waterproof roof   tiles facilitated fundamentally new types of  construction ultimately reflected in the grand   structures of imperial rome fired clay vessels  were used to store and transport liquids and   grains stimulating commerce and most importantly  fired clay tablets served as the world's first   permanent writing medium the surface on which  ancient sumerian cuneiform script was written   but the long-term impact of this discovery was  perhaps even greater once the ancients recognized   that heating clay produced a fundamentally new  material it was only a matter of time before   they began experimenting with other materials  thus they invented lime by heating limestone   charcoal by heating wood various metals by  smelting mineral oils in a sense our modern   field of material science originated with the  discovery of fired clay so many millennia ago   the first man-made metal was copper we  have evidence of its use as early as   9000 bc in the middle east though these artifacts  were apparently made from lumps of relatively pure   copper found in stream beds it was another 5000  years before the production of copper from mineral   mineral ores began copper-rich ores were found  in mesopotamia in anatolia and on the island of   cyprus indeed our word copper comes from the  latin cuprum meaning metal found on cyprus   but these ores couldn't be exploited until ancient  metallurgists develop the process we call smelting   the heating of copper ore with charcoal to produce  pure copper now smelting occurs through a type of   chemical reaction called an oxidation reduction  reaction in which one substance loses electrons   and therefore is said to be oxidized and another  substance gains electrons and is said to be   reduced here's a typical example cuprite in this  chemical formula is copper oxide it's a copper ore   co is carbon monoxide produced by the combustion  of charcoal now at about 2000 degrees fahrenheit   the carbon monoxide molecule pulls an oxygen atom  from the copper oxide to form carbon dioxide gas   and pure copper which is what we're after in  the first place by the way 2000 degrees might   seem pretty hot but it's actually considerably  lower than the temperature required to melt   iron about 2 800 degrees fahrenheit and this  explains why copper was the first metal to be   exploited by humans even though iron is about  1 000 times more plentiful in the earth's crust   copper came first not because of its availability  but because it could be smelted more easily   so why was the production of metals so important  to ancient civilizations well as we've seen metals   are relatively strong and they have more or  less equal strength in tension and compression   metals can also be formed by casting by heating  to the melting point and then pouring the molten   metal into a mold but most importantly metals are  malleable they can be shaped or formed into thin   sheets by hammering in sharp contrast with stone  and clay moreover metals are actually strengthened   by hammering a characteristic that makes them  particularly well suited for tools and weapons   but all of these desirable characteristics come at  a price smelting copper consumes a vast amount of   charcoal for fuel from antiquity until relatively  modern times charcoal was produced in a highly   specialized craft process the collier built a  large conical pile of wood as you can see in this   photo and then covered it with soil and ignited  its core the soil limited the amount of oxygen   available for combustion so the fire burns slowly  driving off water and resins from the wood but   leaving behind porous lumps of nearly pure carbon  a substance capable of burning at a much higher   temperature than wood in antiquity it took about  seven pounds of wood to make one pound of charcoal   and 20 pounds of charcoal to smelt one pound  of copper the grand total is 140 pounds of   wood to smelt a single pound of copper ancient  smelters were voracious consumers of timber   and as metals became ever more popular the  resulting insatiable demand for charcoal   caused widespread deforestation the barren terrain  of modern grease was caused largely by the clear   cutting of forests during the classical era and  subsequent erosion of the irreplaceable topsoil   clearly the environmental impact of technological  development is not just a modern phenomenon   despite the depletion of timber  experimentation with metals continued   around 3200 bc smelters began adding small amounts  of tin to copper to produce a new material bronze   a metal composed of two or more elements is called  an alloy thus bronze is an alloy of copper and tin   a fascinating aspect of the science of materials  is that adding an impurity to a substance often   increases its strength thus an alloy  is typically stronger than both of   its constituent elements and indeed bronze is  considerably stronger than pure copper or pure tin   yet paradoxically the melting temperature  of bronze is actually 140 degrees lower   than that of pure copper and so bronze  is actually better suited for casting   for these reasons bronze quickly superseded copper  as the preferred metal of ancient civilizations   it held that distinction for over a millennium  and in the process it gave its name to a new era   the bronze age during this period homeric heroes  were clad in bronze while bronze plows sickles   and saws improved the lives of common people by  the 10th century bc bronze casting technology was   sufficiently advanced that an artisan named hiram  of tyre was able to fabricate 27-foot tall bronze   pillars for solomon's temple in jerusalem by that  time however bronze was always already giving way   to a new material iron that would define a new age  the earliest iron known to man actually originated   in meteorites and was used as a luxury metal for  several thousand years before the iron age began   indeed we know that the ancient sumerians actually  succeeded in identifying iron's extraterrestrial   source because they called it heaven metal  but sometime in the second millennium bc   smelters in the near east develop techniques for  producing iron from an ore called hematite in this   process hematite was placed on a layer of charcoal  inside a furnace which in its earliest form was   probably just a hole in the ground as you can  see in this graphic but eventually that furnace   evolved into a stone structure built above  ground once the charcoal was ignited air was   blown into the furnace through a clay pipe called  a tweer to increase the combustion temperature   the result was an oxygen oxygen reduction reaction  similar to the one we saw in copper smelting   carbon monoxide rising up through the furnace  reacted with the iron oxide in the hematite ore   to produce iron and a pool of waste material  called slag but while this chemical reaction   theoretically produces pure iron the actual  product of these crude ancient furnaces was   far from pure iron melted about 2 800 degrees  fahrenheit but ancient forges couldn't do much   better than 2200 degrees so the smelting  process produced not a pool of molten iron   but a spongy mass called a bloom composed of iron  some unreacted ore unburned charcoal and other   impurities while the bloom was still red hot then  it had to be hammered vigorously to drive out the   impurities and create a usable metal though  still not a pure one this product was called   wrought iron because it had been wrought  or worked through this hammering process   by the way the other form of iron cast iron  was largely unknown in the ancient world   because the ancient furnaces couldn't achieve  temperatures hot enough to melt iron cast iron   wouldn't come into common use until the medieval  period partly for this reason in antiquity iron   doesn't appear to have been a significant  improvement over bronze the two materials are   comparable in strength bronze because of its lower  melting temperature was actually easier to smelt   and therefore could be used for castings while  iron couldn't iron is significantly harder which   means that iron weapons and cutting tools hold a  better edge than the equivalent bronze instruments   but it's also much more susceptible to  corrosion or rusting and therefore to   the long-term deterioration given iron's lack  of clear-cut advantage then why did the bronze   age yield to the iron age why why did iron  become the metal of choice in the near east   india europe and the far east from around 1200  bc onward the answer is quite simply availability   as i mentioned earlier iron is about 1 000  times more plentiful in the earth's crust   than copper tin bronze's other constituent is even  scarcer than copper indeed archaeological evidence   suggests that severe shortages of tin occurred  during the late bronze age providing a powerful   stimulus for increased iron production because  iron is so much more difficult to smell than   bronze it took a long time for this technology to  mature but once iron became economically viable   the widespread availability of iron ore virtually  guaranteed that iron would surpass bronze and   so it did like most new technologies iron  found its earliest applications in warfare   primarily for weapons and armor but as its  production costs decreased iron was adopted   in all sorts of new civil technologies which  we'll examine is examined in future lectures   like these clamps in stone masonry construction  spikes for fastening ships holes together wheel   rims on wagons in all manner of axles fittings  and connectors in machines like this water wheel   clamps and connectors are small and easy to  overlook but in a very real sense the classical   world was held together with iron i'd like to  conclude this lecture with four important points   first note that all the materials we've talked  about in this lecture were well established   prior to the classical era thus they provided  an essential foundation for greek and roman   technological development second note that we  have not discussed all of the materials that   contributed to technical technological development  in the ancient world we haven't discussed   precious metals like gold and silver which were  used primarily for coins from the 6th century   bc onward now coinage had an enormous influence on  technological development however because precious   metals weren't actually employed in engineered  systems we won't consider them further in this   course we also haven't discussed lead which was  used for specialized applications like water pipes   we'll discuss this material during our lectures on  water supply systems and we haven't yet discussed   the one major engineering material that came  into widespread use during the classical era   concrete this material the heart of the  roman construction revolution will occupy our   attention during lecture six third point even  when we add concrete and lead to our list the   materials available to greek and roman builders  were still very limited both in number and in   their suitability for engineering applications  in sharp contrast with the modern world's immense   and ever expanding array of custom manufactured  metals plastics and ceramics to a large extent   we'll see the genius of ancient engineering in  the use of these extremely limited materials   in ways that capitalize on their unique strengths  and compensated for their inherent weaknesses   final point while we tend to think of materials as  enablers of technological development we've also   seen how ancient systems systems for acquiring  and processing materials are important examples   of technological development in their own  right we'll explore this idea in much greater   depth next lecture when we examine how that most  ubiquitous of all ancient construction materials   stone was quarried transported shaped  and assembled into masonry the very   fabric of the ancient world's most beautiful  and enduring structures until then thank you welcome back you know when we look at an  architectural gem like the temple of athena   nike in athens we tend to focus on the building's  beautiful proportions it's elegant fluted   columns its finely crafted ionic capitals  and the delicate carvings of its entablature   faced with such architectural refinement it's  easy to take the temple's plain masonry walls   for granted after all just a bunch of stone  blocks piled on top of each other right   well maybe but how were those  blocks extracted from solid bedrock   at a time when the most sophisticated  quarrying tool was a simple iron tipped pick   how were they squared shaped and fitted  so perfectly together with only hand tools   without mortar how are they lifted into place  and positioned with such precision well in this   lecture we'll attempt to answer these questions  by following a block of stone from its point of   origin in a quarry to its final resting place in  the wall of a greek temple in doing so will gain   a deeper appreciation of stone as the ancient  world's most important construction material   but more importantly while we tend to think of  materials as enablers of technological development   this story will also illustrate how ancient  systems for acquiring and processing materials   are also important examples of technological  development in their own right and along the   way i hope you'll come to realize that there's  a lot more to stone masonry than meets the eye   now our story begins during  the second millennium bc   during the ascendancy of that great  bronze age civilization of mycenae   in the northern peloponnese the mycenaeans  developed a form of monumental stone masonry   created by piecing together large polygonal  blocks of stone in irregular patterns   with minimal cutting and fitting as we can see  today in the ruins of the citadel at mycenae   later greece called this type of construction  cyclopean because they believed that only the   mythical cyclops could possibly have been strong  enough to move such enormous stones now during   the mycenean era cyclopean construction reached  a very high level of refinement as evidenced   by the famous lion gate shown here but with the  collapse of bronze age civilization around 1200 bc   this technological know-how was lost and not  rediscovered until centuries later now around   the late 8th century bc in archaic era greece  about that same time that the polis emerged   as a political entity greeks once again began  constructing their public buildings of stone   this development was probably stimulated by  a desire for buildings with greater dignity   and permanence but as we've seen it was also  significantly influenced by deforestation the   shortage of timber resulting from increased  demands in metal production and shipbuilding   the earliest of these archaic era stone  structures used polygonal stone construction   probably copied from the ruins of  those bronze age mycedent citadels   but over time greek masonry construction gradually  evolved toward a more refined configuration   of rectangular stones set in horizontal courses or  layers this configuration called ashlar was firmly   established by the 5th century bc once again the  greek's adoption of a new construction technology   was probably not an original idea the greeks were  heavily engaged in seaborne commerce and they're   known to have traded in egypt when where ashlar  construction was already very well established   it's quite likely that greek traders returned  home with stories of monumental pyramids and   temples in the nile valley and these stories  inspired greek architects to begin experimenting   with ashlar masonry certainly we can see  egyptian influence in greek architecture   note the strong similarity in the overall form of  the egyptian temple of ahmanet karnak on the left   and this typical early greek temple on the  right but while greek techniques for quarrying   and building in stone were probably borrowed  from the egyptians the greeks made substantial   improvements to these methods over time the  great philosopher plato acknowledged this   point when in the 4th century bc he wrote that  the greeks had invented nothing rather they had   borrowed all of their technologies from other  peoples but then had improved on everything   well let's delve more deeply into the fully  evolved greek system of stone masonry construction   by following a block of marble from quarry to  temple wall greece has always had an abundant   supply of limestone and marble for building  limestone is a sedimentary rock usually formed   from the accumulated skeletal fragments  of marine organisms like coral   it's found in many forms from soft porous tufa  to travertine which is nearly as hard as marble   marble is a metamorphic rock created when  limestone is subjected to intense heat and   pressure deep below the earth's surface marble  is strong hard and found in an amazing variety of   beautiful colors it was first incorporated into  greek architecture in the early 6th century bc   and soon became the preferred material for  important public structures in athens the great   building program instituted by pericles in the 5th  century bc a program that included extraordinary   structures like the parthenon and the propilea was  supplied largely from two quarries one at mount   high meadows seven miles southeast of athens  and one at mount pentelicon nine miles to the   northeast the close proximity of these quarries  to athens was no accident because classical era   greece was primarily a seafaring civilization most  of its roads were little more than dirt tracks   long distance transport of heavy stone blocks  over these poor roads was out of the question   and so quarries either had to be close to  the construction projects they were supplying   or close to navigable waterways ancient quarries  like mount pentelicon were often located on   hillsides so that blocks of stone could be  extracted in a stair-step pattern and then   lowered down the hillside for sub

2022-09-20

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