Basilica
The Latin word basilica was originally used to describe a Roman public building, usually located in the forum of a Roman town. In Hellenistic cities, public basilicas appeared in the 2nd century BC. After the Roman Empire became officially Christian, the term came by extension to 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
In architecture, the Roman basilica was a large roofed hall erected for transacting business and disposing of legal matters. Such buildings usually contained interior colonnades that divided the space, giving aisles or arcaded spaces at one or both sides, with an apse at one end (or less often at each end), where the magistrates sat, often on a slightly raised dais. The central aisle tended to be wide and was higher than the flanking aisles, so that light could penetrate through the clerestory windows. One can determine a basilica apart from other structures by its dome. 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).
Uses
Probably the most splendid Roman basilica is the one constructed for traditional purposes during the reign of the pagan emperor Maxentius and finished by Constantine 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).