The Roman were very good builders, engineers and town planners. They invented concrete as a building material by mixing gravel, sand and cement.
The Romans further developed the arch which was first used by Etruscans or bridges. They used it for vaults (long hallways with a semi-circular roof) and for creating domes.
Domes were used in Basilicas, which were large, covered halls used as courts of justice and for banking and other commercial transactions. The largest of these domes was completed in Rome by the emperor Constantine in AD 311.