So I’m taking a course in Graeco-Roman Engineering at the moment...
And I’m (re)learning about Opus Testaceum, the method of building construction that the Romans heavily favored during the Imperial period, throughout their empire, and it got me to thinking, and I wanted to come share some of my thoughts.
To begin with a little background, over the incredibly long course of their civilization (c.700 BCE to 1500 CE as an independent power, although identification with Roman civilization and ethnicity continued well into the 1900s CE.) the Romans used a variety of stone-working and masonry techniques to construct the buildings that made up their cities and their permanent fortifications all over the Mediterranean world (and its hinterlands.) Art historians and archaeologists make a big deal of knowing the different kinds of masonry that the Romans used in order to try and date buildings and monuments and foundations to the period in which they were constructed. For example, in Pompeii, by analyzing only the kinds of masonry used in the construction of surviving structures and foundations, it’s possible for art historians and archaeologists to look at a thing and draw an initial assessment of whether it was built during the city’s independent Oscan phase, its Samnian occupation, its early days in the Roman Republic, or its time as a city of Imperial Rome.
Each of the different masonry phases above (and a couple subdivisions beneath) are known as a separate form of masonry construction, and are named thus: Opus Techniquous. (Where Techniquous = whatever the pithy latin word is for the kind of building technique being used.) The names are pretty straight-forward and kinda self explanatory: for example, Opus Quadratum is -
an ancient Roman construction technique, in which squared blocks of stone of the same height were set in parallel courses, most often without the use of mortar. The Latin author Vitruvius describes the technique. (pictured below.)
Opus Testaceum, by comparison, is best summarized thus:
Wall built with concrete (Opus Caementicium) poured between courses of specially-made triangular-shaped bricks.
Why build a wall this way? In a word: durability. Common sense would suggest that a wall built of neatly-fitting square blocks would be sturdier than one constructed in the manner above, but in reality, simple stone walls with mortar are very fragile (comparatively) because they don’t have a lot of give in them. The structure that makes them up doesn’t absorb stress over time as well – once a portion of the wall is compromised or weakened, the whole structure could collapse because all of the blocks are being held up by the other blocks.
On the other hand, the cement poured between the courses of triangular bricks used in Opus Testaceum holds together even when individual portions are weakened or compromised. It absorbs stresses over time much better, and is as a result a far more durable form of construction.
But it wasn’t just the durability of Opus Testaceum that made it so ubiquitous during the Roman Period. The Romans had other construction methods that were nearly as durable or even in some cases potentially more durable. However, one thing that Opus Testaceum had over its fellow masonry styles and that made it the preferred method of building in the Mediterranean during the Roman period was that it was mass-producible.
Counter-intuitively from our modern perspective, the level of ability it took to build stone walls with bricks and concrete (as in Opus Testaceum) was far lower than the level of ability it took to build them out of stones and mortar. Although the ease with which Lego walls can be build out of similarly sized and shaped square or rectangular blocks certainly misled me to believe that it was far easier to build a wall with uniformly square, shaped blocks piled on top of each other at first blush, it should be borne in mind that Lego blocks stick together because they have those small around pegs and holes that allow them to fit into one another as well as on top of one another. Today plastic bricks with those pegs and holes can be easily made with plastic, but in the Ancient World it took an enormous amount of skill with shaping stone to shape ‘seemingly square or rectangular’ bricks in subtle ways that allowed structures built of square or rectangular bricks to hold up and ‘stick together.’ The work was very slow, very painstaking, and each block was a miniature project in and of itself. Special tradesmen known as stone-cutters and stone-masons made their living in this way. There are unfinished temples all over Greece and Sicily that attest to the enormous technological skill cost and time investment required in building this way.
On the other hand, a Roman wall built using Opus Testaceum really needs nothing aside from some specially-made triangular bricks and some concrete to pour between them. Almost anyone can take orders from a master builder and stack bricks on top of a fresh layer of mortar and then pour cement in between them and jab loose stones and gravel down into it to harden the mix. Special ‘dressing’ can be attached to the outside of such walls very easily, as well. Infact, the Ancient Roman Imperial army had something of a reputation for being a lot like the U.S. Army’s Corps of Engineers in that when they weren’t busy training or campaigning legionaries could easily be put to use building necessary structures in just such a fashion. (There are bricks all over the Empire that bear the marks of the legions responsible for their creation and employment.)
It was far easier, and cheaper, and quicker to build something using Opus Testaceum, in part because the labor could broken up and completed in pieces, in mass quantities, and then assembled on site by unskilled workers (not that the Roman soldiery was unskilled: they were quite professional and adept, but really, anyone could walk in off the street and get paid to help build something for a day.) Brick-makers could bake triangular bricks in a number of sizes in huge batches without any idea when they’re going to be used or by whom or any real need to know either of those things in advance. The mixture to make concrete could be prepared well in advance of actually being used. These two products could then be shipped and sold all over the empire at low prices (due to mass production) and entire buildings could go up within a matter of months by just combining sufficient quantities of the two with a large, unemployed work force and a handful of skilled architectural overseers.
This made Opus Testaceum the building method of choice across the Roman world during the Imperial period.
I say during the Imperial period, because it was unique to the Roman Imperial period in the Mediterranean that mass-production could be utilized to such a scale. At no time in world history before (or since, before the modern era removed such limitations on long-distance trade) had a single power controlled the entire Mediterranean, making quick, secure, and reliable methods of trade (necessary to the functioning of a mass-production economy) possible.
In the absence of mass-production, each local city or community in a region needed to have enough skilled tradesmen on hand to produce whatever the community needs, whenever the community needs it, on demand. Like with above example of the Greek temples and skilled stonemasons - each community that wanted to build something would need a set of skilled stonemasons who could do the work. They would hire less-skilled workers, and the work with be slow because each piece needed for the work would have to be made on demand (with nothing lying around beforehand.) Projects could expect to take decades, even centuries. Some might never be completed at all.
Other trades operated in a similar fashion: if you needed some kind of metal working done, you had to go to the local, community metallurgists to have them make it, special-order, for you. It would cost more, the metallurgists in question might not be very good, and it could take quite a while for them to complete your order. Carpentry, sculpture, and so on – all the trades would work relatively the same.
A large number of cities in a small area could in some ways overcome these short-comings by relying on inter-community trade: someone from city A could go to city B and hire their stonemasons or metallurgists if city A had none or theirs were already busy or theirs were not as good. But the problem with such a system was that this kind of inter-community trade could often break down if any of the cities involved, or even other cities in the neighborhood, began fighting with one another over territory, resources, or some other problems. And even when there was peace, a handful of cities within a small area does not begin to equal the pool of talent that was the Roman Empire at its height, stretching from Britain in the far north-west to Egypt in the east and comprised of roughly 60 million inhabitants (not to mention the millions of cross-border workers the empire employed for one thing or another.)
The Roman Empire, by unifying the entire region in a relatively peaceful state of affairs (in comparison to the periods that would come before and after) and encouraging trade beneath its umbrella, made it possible for a buyer in Arles, in Southern Gaul (France) to contract with brick-makers in Barcelona, while also buying high-quality concrete mixes from supplies in Pisa. Or for a general merchant in Rome to import huge numbers of mass-produced pottery from kiln factories in North Africa. Or for a Syrian tabernae of the highest class to buy Falernian wine for its customers.
Instead an economic reality in which each city or local community had to have a craftsman of every variety, the Empire created a system in which tradespeople could be scattered across the empire and still serve clients hundreds of miles away. In fact, the Romans got so good at this system of mass production that they basically did away with the previous economic model entirely: with North African kilns producing huge amounts of quality pottery for the empire, very few other centers of pottery production even existed – except on a very small scale and for only local concerns. Stonemasons never quite went away entirely, but their methods of construction were no longer quite as in demand (except for extremely high-quality, aesthetically-pleasing constructions paid for by the super-rich) and they largely concentrated in the rich, wealthy major cities of the Empire. Other trades went the same way.
So can you imagine what happened to the economy of the Roman world when the security of this vast, interconnected trading network went away over the course of the Fifth Century CE? The result, to put it baldly, was wide-scale economic collapse, and a quick dying-off of the specialized technological know-how that made the system possible. Once Rome could no longer guarantee the safety of shipments from North Africa to the rest of the Empire, merchants in the rest of the empire who depended on shipments of North African pottery to sell to their customers either went broke, or had to turn to local, less-skilled potters for supply. The technological refinement of African potters, no longer an exportable commodity, gradually went extinct and more-coarse, less-refined forms of potter gradually replaced it.
Technologies that depended on a number of smaller pieces being put together to create a technologically-advanced hole went out the window even faster: the brick-makers who supplied the triangular bricks couldn’t make any money selling bricks if their customers couldn’t also buy the cement mixture they needed to make walls using Opus Testaceum, so they gradually stopped making those bricks. Similarly, the cement mixers gradually went out of business as their mixes could no longer be reliably exported to anyone who had sufficient bricks to use them. To this day modern scientists what exactly the Romans did to make their cement, which is by many accounts far superior to a number of modern forms of cement. Other specialized craft and technological knowledge also vanished during this period as the system that allowed for this kind of specialized craft development went away and no one stepped in to find a way to recreate it on a smaller scale. Cheap, mass-produced goods and services went out the window.
Not that the system disappeared overnight or anything: in the East, where the Roman Empire survived the Fifth century and well into the Seventh with a thriving economy, technological specialization and mass-production continued, albeit on a somewhat smaller, more-local scale. And in places like Italy and Gaul and urban Hispania and North Africa, networks of large cities boasted a few generations of specialized craftsmen who could keep low-levels of economic specialization and mass-production going, until funds dried up and clients from overseas markets stopped calling entirely. The more urban parts of the old Empire didn’t so much as collapse economically as they did transition towards a new model of economic production, in which relatively-unrefined products were produced locally for the people who could afford them, while the sufficiently wealthy could still afford to send large amounts of money far from home to pay for the very best craftsmanship that money could buy.
But this does help to explain why technology across the old Empire (in the West, especially) seems to go backwards in the archaeological record of the early medieval period, and why in especially remote places such as Britain we have people writing a few hundred years later, when remarking upon the ruins of ancient Roman buildings, that only giants could have built such structures. There was simply no one left in the former province who knew how to build something on that scale - stone-masonry had never quite reached Graeco-Roman heights even before the Roman conquest, and during the Roman Imperial period it wasn’t necessary: Opus Testaceum meant that a few hundred poor citizens with no training at all could work under a single master builder to put together a brick and concrete structure in no time. Then once the mass-production economy that made such things possible went away, the knowledge and technological specialization required to build them simply no longer existed, and in many places (such as Britain) had not existed for such a long time that people began to think of it as mythical, and began to ascribe such constructions to superhuman powers.
Makes one think.