From the Enc. Brittanica: "Italian Terme di Caracalla , ancient (Latin) Thermae Antoninianae (“Antonine Baths”) public baths in ancient Rome begun by the emperor Septimius Severus in AD 206 and completed by his son, the emperor Caracalla, in 216. Among Rome's most beautiful and luxurious baths, designed to accommodate about 1,600 bathers, the Baths of Caracalla continued in use until the 6th century. The extant ruins, together with modern excavations and restorations (including conspicuous reconstructions), are the most extensive of any surviving Roman bathing establishments and consist centrally of a block of large vaulted bath chambers covering an area of 750 by 380 feet (230 by 115 m), with courts and auxiliary rooms, surrounded by a garden with space used for exercise and games.

There were three main bath chambers: the frigidarium, or cold room; the caldarium, or hot room; and the tepidarium, or lukewarm room. Between the frigidarium and the tepidarium was the great hall, roofed by an enormous vault with clerestory windows, a prototype of the vaulted naves of the medieval churches. There were also large open-air swimming pools. Marble was used lavishly, and sculpture, mosaics, frescoes, and other decorations ornamented the interior.

In the summertime, the Baths of Caracalla are the site of open-air opera performances, employing spectacularly large casts for such operas as Aida and Carmen."