The Thermae Antonianae is one of the most impressive and better preserved thermal complexes of ancient times. They were constructed on the initiative of Caracalla (211 – 217 A.C.) West of the via Appia. The central building was started in 212 and completed in 216. It stretched on a rectangular surface and had a series of main premises on the minor axis: frigidarium, basilica, tepidarium and calidarium. The entrances, the vestibules and the palaestrae were symmetrically located on this premises’ side. The external enclosure, porticus, constructed by Caracalla’s successors Elagabalus (218 – 222 A.D) and Alexander Severus ( 222 – 235 A.D.) bounded a squared area of 330 meters by side. A two-floor portico composed the north side of the enclosure and half of the east and west sides. The other half was composed of an exedra inside which various vaulted premises would open on. The south side of the enclosure was composed of a large two-floor cistern divided in 64 vaulted premises. This cistern supplied the Aqua antoniana Iova, a branch of the Aqua Marcia aqueduct. The baths ceased definitively to be used in 537 when the Goths cut off the aqueduct.