large, roofed hall in Rome, begun by the emperor Maxentius and finished by Constantine about AD 313. This huge building, the greatest of the Roman basilicas, covered about 7,000 square yards (5,600 square m) and included a central nave that was 265 feet (80 m) long and 83 feet (25 m) wide.

The basilica followed in construction and plan the great hall of the Roman baths. The vaults over the bays on the north side are still to be seen overhanging without support, a striking testimony to the marvelous cohesion and enduring strength of Roman concrete construction.