Ancient Roman architecture
Although concrete had been used on a minor scale in Mesopotamia, Roman architects perfected Roman concrete and used it in buildings where it could stand on its own and support a great deal of weight. The first use of concrete by the Romans was in the town of Cosa sometime after 273 BC. Ancient Roman concrete was a mixture of lime mortar, aggregate, pozzolana, water, and stones, and was stronger than previously-used concretes. The ancient builders placed these ingredients in wooden frames where they hardened and bonded to a facing of stones or (more frequently) bricks. The aggregates used were often much larger than in modern concrete, amounting to rubble.
Formwork
Some of the earliest examples of concrete slabs were built by Roman engineers. Because concrete is quite strong in resisting compressive loads, but has relatively poor tensile or torsional strength, these early structures consisted of arches, vaults and domes. The most notable concrete structure from this period is the Pantheon in Rome. To mould this structure, temporary scaffolding and formwork or falsework was built in the future shape of the structure. These building techniques were not isolated to pouring concrete, but were and are widely used in masonry. Because of the complexity and the limited production capacity of the building material, concrete’s rise as a favored building material did not occur until the invention of Portland cement (and developments by the Edison Portland Cement Company) and reinforced concrete.