Roman basilicas

A Roman basilica was a large public building with several functions, typically built alongside a town’s forum (Wikipedia). Courts met there, other official and public business was done there, and, like the baths, it displayed honorific statues. The form is a rectangular hall: a central nave flanked by two or more aisles, the roof higher over the nave so that light came in through a clerestory, and an apse at one end that held the raised tribunal where the magistrates sat.

The word comes from the Greek basilikḗ stoá, “royal stoa”. The first known basilica in Rome was the Basilica Porcia, built in 184 BC; the basilica at Pompeii, from about 120 BC, is described as the earliest to survive. The last civic basilica built in Rome was that of Maxentius, begun in 306 or 308 and finished under Constantine, which roofed its hall with brick-and-concrete cross-vaults instead of timber.

Because a basilica could hold a large crowd, the early church adapted the plan for worship, and by the end of the 4th century it had become the normal plan for churches: nave, aisles, clerestory and apse, usually under a timber roof. This is why many churches are still called basilicas.

The basilica in this atlas under this heading is the underground one beside Porta Maggiore in Rome, a hall of the 1st century AD in the basilica plan that lies below ground. Its page says what survives, how to get in and how rarely the door is open.