The period of focus here is the Archaic (ca. sixth century BC) and Republican (ca. fifth to first centuries BC) eras, when the dominant technique for monumental construction in the city of Rome was ashlar masonry, that is, construction using tightly fitted squared stone blocks. We have very little contemporary written evidence relating to construction from this period. The most important surviving source is the architect Vitruvius, whose ten books on architecture were written early in the reign of Augustus, probably in the 20s BC, but which represent a compendium of knowledge from previous generations, albeit sometimes in idiosyncratic ways. Beyond Vitruvius and occasional passages in other authors, as well as rare iconographic evidence, we have to rely on archaeological evidence from the remains of the buildings themselves to understand Roman construction technology. While in general terms the range of technologies available to Roman builders of this period was more or less the same as that used in the contemporary Greek world and the eastern Mediterranean, the specifics of local geology and culture resulted in a distinct Roman tradition.
Getting tuff
The landscape around Rome is a volcanic one, shaped by the powerful prehistoric (600,000 to 36,000 years ago) eruptions of two volcanic systems north and south of the city. These volcanic deposits were in turn eroded by the Tiber and its tributaries, which cut deep channels in the topography. The so-called seven hills of Rome owe their existence to the interaction of these processes.
Many of these, sometimes referred to in English as ‘tufa’; this latter term, however, should be reserved for a variety of limestone), which can be formed by pyroclastic flows, pyroclastic surges, or the consolidation of ash thrown out by the eruption, and hence is distinct from lava. Tuff is a soft stone that is relatively easy to cut and shape, making it ideal for the production of ashlar blocks. The specific properties of each eruption create different characteristics (hardness, density, colour, etc) in the resulting tuff. Over the course of the Archaic and Republican periods, Roman builders and their neighbours came to recognize these different properties and employed different varieties of tuff in the situations for which they were best suited. (This knowledge was also eventually put to good use with the development of concrete masonry; for instance, the aggregate used in the concrete dome of the Pantheon includes progressively lighter types of stone.) We can understand this selective use itself as a technological development, made possible by the geological diversity of the territory around Rome as well as the Roman incorporation not just of the territory itself but also local knowledge of that territory.
