The column of Phocas, erected in honour of the Byzantine emperor who was the contemporary of Gregory the Great, faces us, and to the right are the columns of the temple to Antoninus Pius and Faustina, now the facade of the church of San Lorenzo in Miranda. The columns are of _cippolino_ marble. See page 32.] The era of _thermae_ or public baths began with Agrippa in 27 B.C., and by the end of the third century eleven such existed in Rome exclusive of the smaller baths or _balnae_, of which there were 850. Nero, Titus, Trajan, Septimius Severus, Caracalla, Diocletian, were all builders of _thermae_. These huge edifices were a great deal more than public baths. They were a Roman form of the _gymnasia_ of the Greeks, and the colossal ruins that remain can give but the barest idea of what they must have been at their best. They included immense halls and courts for athletic displays, vestibules, concert rooms, picture galleries and libraries, pleasure grounds decorated with statues fountains and shrubs and surrounded by open porticoes. Feasts, concerts, and entertainments were provided, and pleasant hours could be whiled away within their walls by the gilded youth of Rome. The baths of Diocletian, of which the church of S. Maria degli Angeli is a magnificent fragment, could accommodate 3600 bathers at a time, those of Caracalla 2000. An army of slaves and attendants waited upon the bathers and sped upon their errands along underground passages from one end of the building to the other. Ruins of the _thermae_ of Caracalla and of Titus are still standing. Out of the colossal vaults and walls of Diocletian's baths have been constructed two churches, a monastery, a large museum, and a variety of storehouses, warehouses, stables, and cellars. Equally remarkable was the Roman system for supplying their city, their _thermae_, and their 1350 street fountains with pure water. Appius Claudius was the first to collect the water from springs amongst the mountains in the neighbourhood of Rome and to bring it across the campagna. This was in 313 B.C., up to which date the inhabitants of the city had depended for their water supply upon the Tiber and upon sunken wells. Following in the steps of Claudius, fourteen aqueducts whose united length measured 360 miles were built at various times. They varied in length from 11 to 59 miles and their course lay sometimes under ground and sometimes 100 feet above it, while the amount of water they poured daily into Rome has been estimated at 54,000,000 cubic feet. Four of these ancient aqueducts are still in use. The Virgo, built by Agrippa in 27 B.C., and now known as the Trevi; the Alexandrina, constructed by Alexander Severus (222-235), probably to supply his own baths, and now known as the _acqua Felice_; the ancient Trajana, now Paola, and the Marcian, restored by Pius IX. The Marcian was always considered the best drinking water, and the Trevi being a softer water was preferred for bathing purposes.