Baths of Diocletian
The Baths of Diocletian (Thermae Diocletiani) in Rome were the grandest of the public baths, or thermae built by successive emperors. Diocletian's Baths, dedicated in 306, were the largest and most sumptuous of the imperial baths and remained in use until the aqueducts that fed them were cut by the Goths in 537. Similar in size and plan to those of Caracalla, they are well preserved because various parts later were converted to ecclesiastical or other use. The complex now houses the basilica of Santa Maria degli Angeli e dei Martiri (in the tepidarium), the church of San Bernardo alle Terme (in one of the two circular rooms), and part of the Museo Nazionale Romano (National Roman Museum). The three soaring vaults of the basilica's transept provide, one of the few glimpses of the original splendor of Roman building. It was oriented to the southwest so that solar energy heated the caldarium without affecting the frigidarium. Other remains of the baths are visible several streets away.

From: www.wikipedia.org