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.
Modern architecture
French industrialist François Coignet was the first to use iron-reinforced concrete, that is, concrete strengthened with iron bars, as a technique for constructing buildings. In 1853 Coignet built the first iron reinforced concrete structure, a four-story house in the suburbs of Paris. A further important step forward was the invention of the safety elevator by Elisha Otis, first demonstrated at the Crystal Palace exposition in 1852, which made tall office and apartment buildings practical. Another important technology for the new architecture was electric light, which greatly reduced the inherent danger of fires caused by gas in the 19th century.