The Latin word basilica (derived from Greek, Basiliké Stoà, Royal Stoa), was originally used to describe a Roman public building (as in Greece, mainly a tribunal), usually located in the forum of a Roman town. In Hellenistic cities, public basilicas appeared in the 2nd century BC.

Basilicas were also used for religious purposes. The remains of a large subterranean Neopythagorean basilica, dating from the 1st century, were found near the Porta Maggiore in 1915; the stuccoes on the interior vaulting have survived, though their exact interpretation remains a matter for debate. The groundplan of Christian basilicas in the 4th century were similar to that of this Neopythagorean basilica, which had three naves, and an apse.

After the Roman Empire became officially Christian, the term came by extension to specifically refer to a large and important church that has been given special ceremonial rites by the Pope. Thus the word retains two senses today, one architectural and the other ecclesiastical.

Architecture

The oldest known basilica, the Basilica Porcia, was built in Rome in 184 BC by Cato the Elder during the time he was censor. Other early examples include the one at Pompeii (late 2nd century BC).

Probably the most splendid Roman basilica (see below) is the one constructed for traditional purposes during the reign of the pagan emperor Maxentius and finished by Constantine I after 313. As early as the time of Augustus, a public basilica for transacting business had been part of any settlement that considered itself a city, used like the late medieval covered markethouses of northern Europe (where the meeting room, for lack of urban space, was set above the arcades).

Basilicas in the Roman Forum

• Basilica Porcia: first basilica built in Rome (184 BC), erected on the personal initiative and financing of the censor Marcus Porcius Cato (Cato the Elder) as an official building for the tribunes of the plebs
• Aemilian Basilica, built by the censor Aemilius Lepidus in 179 BC
• Julian Basilica, completed by Augustus
• Basilica Opimia, erected probably by the consul Lucius Opimius in 121 BC, at the same time that he restored the temple of Concord (Platner, Ashby 1929)
• Basilica Sempronia, built by the censor Tiberius Sempronius Gracchus in 169 BC
• Basilica of Maxentius and Constantine (308 - after 313)

Palace basilicas

In the early Imperial period, a basilica for large audiences also became a feature in the palaces. In the 3rd century AD, the governing elite appeared less easily in the forums. "They now tended to dominate their cities from opulent palaces and country villas, set a little apart from traditional centers of public life. Rather than retreats from public life, however, these residences were the forum made private." (Peter Brown, in Paul Veyne, 1987). Seated in the tribune of his basilica the great man would meet his dependent clientes early every morning.