public baths in ancient Rome begun by the emperor Septimius Severus (Severus, Septimius) 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 metres), 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 medieval churches. There were also large open-air swimming pools. Marble was used lavishly, and sculpture, mosaics, frescoes, and other decorations ornamented the interior.

These magnificent baths have continued to influence architects through the centuries. In the Renaissance, Donato Bramante (Bramante, Donato) and Andrea Palladio (Palladio, Andrea) used them as inspiration for grand structures. And in the 20th century the architectural firm McKim, Mead & White incorporated elements from the baths—especially from the ceilings—into their design of the first Pennsylvania Station in New York City (built 1910, demolished 1964).

The Baths of Caracalla are now the site of summertime open-air performances of ballet and opera, including works that employ spectacularly large casts, such as Giuseppe Verdi (Verdi, Giuseppe)'s Aida and Georges Bizet (Bizet, Georges)'s Carmen.