What architectural element was perfected by the Romans and enabled them to build public buildings such as the Pantheon?

Answer 1

There were three elements, not one.

The Romans effected what historians call the Roman architectural revolution or concrete revolution. This involved the extensive use of concrete, the barrel (simple) arch and the vaulted arch. These three elements enabled the Romans to go beyond Greek methods of construction which used cut-stone and post-and-beam or post-and-lintel structures. They became essential for large roofs and large buildings, such as basilicas (public buildings) amphitheatres (arenas), theatres, baths, domes and forts and fortifications. They also made it possible to build bridges which were much longer than before and could cross much wider rivers and valleys.

Prior to the Romans concrete was hardly used. The Romans were the first to made large scale use of it. They developed a type of concrete (opus caementicium) which was as resistant as modern concrete. It also set underwater and therefore could be used to build docks for ports, dams and bridges. It was less fluid than modern concrete and had to be layered by hand. It was made with a mortar made by mixing a volcanic rock called pozzolana (which is named after Pozzuoli, a suburb of Naples) with lime. Rubble from stones, bricks or pottery sherdrs were added as aggregates which added body to it. Concrete had technical and practical advantages. It was exceptionally strong. it could be moulded and could span great distances when shaped into arches, vaults and domes. It was layered into a formwork and it took the shape of its container. It did not require skilled labour and therefore was cheaper.. It was much faster for construction than laborious masonry walls. It was safer because concrete vaulted roofing was fireproof, unlike the wooden-beamed roofs of traditional post-and-lintel construction methods.

The potential of the previously very little used arch and vault, were also fully exploited for the first time. The Romans were the first to fully appreciate the advantage of these structures and make large scale use of them. The Etruscans are thought to have invented the simple (barrel) arch. The oldest example of the vaulted arch has been found in the Greek city of Pergamon (in western Turkey). The (simple, barrel) arch has a strong load- bearing capacity and was useful to build large walls without using the post-and-lintel method and to build bridges which were much longer than ever before. The vault (vaulted arch) has an even greater load-bearing capacity and its structure is suited to support large roofs. Their construction in concrete made them easier to build and even stronger. This led to the use larger and monumental arches and vaults on a grand scale. However, the Romans did not abandon masonry arches and vaults. The vaulted arch came into two forms: the groin arch is formed by two to four intersecting barrel (simple) arches and the rib arch, where the intersecting arches were of different diameter.