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. Source: wikipedia.

http://en.wikipedia.org/wiki/Baths_of_Diocletian