The History Of Greek and Roman Technology - Part 1
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
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