Tuesday, January 16, 2007

Basics in Roman Building Materials and Engineering

Paige Elegy
Honors in Rome - Winter 2007
Small Presentation

Roman architecture is composed mostly of Greek and Etruscan elements. They borrowed the arch from the Etruscans, decorated in the Greek style, and even concrete had been around since Mesopotamian times. However, the Romans were the first to use these elements on a grand scale, and they refined and developed these techniques, leading to the long-standing, memorable monuments we see today.

Early on, the Romans used bricks, both sundried (2nd c BC) and kiln-baked (1st c AD) for most buildings. Stone or brick facings were separated and filled with rubble or packed with clay to form the walls. For larger monuments, they would use huge stone blocks, usually of tufa, a fairly lightweight volcanic stone. These were originally built without anything to hold them together except their own weight. Later on, iron and bronze clamps were used to join the blocks. The clamps were pillaged during the Dark Age and melted down. Since the monuments are still standing, we know that the Romans didn’t actually need the clamps.

Around 273 BC, the Romans began to use concrete. Their first concrete, opus caementicium, was made by mixing lime, sand, water and stones. They would then pour this into a frame and face it with brick or stone. When it hardened, they removed the frames and ta-da!, a wall was born. These materials were easy to find and transport, and the frames could be reused, allowing for fast, efficient building. The walls were usually then faced with stucco or marble, disguising their inner appearances. Now, most of those facings are gone, leaving us with the interiors of the walls. From this, we can see that the Romans used many different styles to adhere the brick facing to the concrete. Some were stronger than others, and some were more decorative. The opus testaceum, used during the Age of Augustus (1st c AD), was rarely plastered, since it looked exactly like a brick wall.

By adding a volcanic ash, pozzolana, to the concrete, the Romans could even get it to set underwater. To keep it from shrinking as it set, they would add horsehair, and to make it more frost resistant, they would add blood. This strong, high-quality concrete allowed the Romans to experiment with various building types and forms.

On of the forms that Romans are famous for is the arch. Used for support and decoration, the arch was widely utilized by the Romans. An arch is built from an odd number of blocks (voussiors), the topmost being the keystone. The beauty of this design is that the more weight presses in and down on the arch, the tighter it holds together. Left by themselves, they have a tendency to bow out, but when pressed, they become firmly locked. The aqueducts are a great example of the use of the arch. Not only do arches allow movement underneath the aqueduct, they require much less building material than a solid wall. The pipes in the aqueduct were lined with cement to keep the water in, and covered to keep it from evaporating or being contaminated.

From the arch, the Romans developed the vault, and arched roof of a building. Starting the 1st c AD, they could actually cast the ceiling as a solid mass, creating a vault that required no buttressing. This made for impressive buildings with an open, airy feel, when compared to the flat-roofed, column supported Greek and older Roman style buildings. The vault was even further developed in the Middle Ages, moving the weight to two and even four walls.

Finally, the Romans revolutionized road building. They were the first to place roads on foundations, and even had ditches on the side for water runoff. The roads were paved and show signs of heavy use (wheel ruts) that we can still see today. They were wide enough to accommodate a two-horse chariot, and had areas on the side for passing and pulling over. Some of these roads are even still used today. Hooray for Roman engineering!