Roman architecture was unlike anything that had come before. The Persians, Egyptians, Greeks and Etruscans all had monumental architecture. The grandeur of their buildings, though, was largely external. Buildings were designed to be impressive when viewed from outside because their architects all had to rely on building in a post-and-lintel system, which means that they used two upright posts, like columns, with a horizontal block, known as a lintel, laid flat across the top. A good example is this ancient Greek Temple in Paestum, Italy.
Since lintels are heavy, the interior spaces of buildings could only be limited in size. Much of the interior space had to be devoted to supporting heavy loads.
Roman architecture differed fundamentally from this tradition because of the discovery, experimentation and exploitation of concrete, arches and vaulting (a good example of this is the Pantheon, c. 125 C.E.). Thanks to these innovations, from the first century C.E. Romans were able to create interior spaces that had previously been unheard of. Romans became increasingly concerned with shaping interior space rather than filling it with structural supports. As a result, the inside of Roman buildings were as impressive as their exteriors.
Materials, Methods and Innovations
Long before concrete made its appearance on the building scene in Rome, the Romans utilized a volcanic stone native to Italy called tufa to construct their buildings. Although tufa never went out of use, travertine began to be utilized in the late 2nd century B.C.E. because it was more durable. Also, its off-white color made it an acceptable substitute for marble.
Marble was slow to catch on in Rome during the Republican period since it was seen as an extravagance, but after the reign of Augustus (31 B.C.E. – 14 C.E.), marble became quite fashionable. Augustus had famously claimed in his funerary inscription, known as the Res Gestae, that he “found Rome a city of brick and left it a city of marble” referring to his ambitious building campaigns.
Roman concrete (opus caementicium), was developed early in the 2nd c. BCE. The use of mortar as a bonding agent in ashlar masonry wasn’t new in the ancient world; mortar was a combination of sand, lime and water in proper proportions. The major contribution the Romans made to the mortar recipe was the introduction of volcanic Italian sand (also known as “pozzolana”). The Roman builders who used pozzolana rather than ordinary sand noticed that their mortar was incredibly strong and durable. It also had the ability to set underwater. Brick and tile were commonly plastered over the concrete since it was not considered very pretty on its own, but concrete’s structural possibilities were far more important. The invention of opus caementicium initiated the Roman architectural revolution, allowing for builders to be much more creative with their designs. Since concrete takes the shape of the mold or frame it is poured into, buildings began to take on ever more fluid and creative shapes.
The Romans also exploited the opportunities afforded to architects by the innovation of the true arch (as opposed to a corbeled arch where stones are laid so that they move slightly in toward the center as they move higher). A true arch is composed of wedge-shaped blocks (typically of a durable stone), called voussoirs, with a key stone in the center holding them into place. In a true arch, weight is transferred from one voussoir down to the next, from the top of the arch to ground level, creating a sturdy building tool. True arches can span greater distances than a simple post-and-lintel. The use of concrete, combined with the employment of true arches allowed for vaults and domes to be built, creating expansive and breathtaking interior spaces.