The plan of the camp can still be traced. It resembled that of the Prætorian camp at Rome, in being a quadrangular space rounded off at the corners. The two longer sides extend from the Church of S. Paolo at Albano to the round Temple, now the Church of S. Maria. One of the shorter sides was parallel to the Appian Road, and the other ran near the Church of S. Paolo. There were four terraces or levels in the camp rising towards the hill behind. The Porta Decumana was in the north-eastern side, and the Porta Prætoria on the south-western. The great reservoirs for water stand on the northern side near S. Paolo, and the thermæ towards the south-east on the opposite side of the Appian Road. At the western corner is the round building usually called the Temple of Minerva, and supposed to be that alluded to by Suetonius as annually visited by Domitian. This round building is in good preservation, but its purpose cannot be determined with certainty. Nibby says that the ancient mosaic pavement still remains at a depth of six feet below the present surface. The amphitheatre is situated between the Church of S. Paolo and that of the Capuchin Convent. It is principally constructed of opus quadratum, but the interior parts are of a mixed masonry, consisting of bricks and fragments of the local stone. This amphitheatre is supposed to have been the scene of the feats performed by Domitian, in killing with his own hand hundreds of wild beasts with arrows and javelins, and also of the degradation of Acilius Glabrio, who was forced, according to Juvenal, by Domitian to join him in these sports of the arena. [Illustration: Plan of the ALBAN HILLS & GABII] Between Castel Gandolfo and Albano four magnificent terraces, rising one above the other, were traced by Cav. Rosa as forming part of the Albanum Cæsarum, and in the Villa Barberini there is a considerable part of a cryptoporticus, ornamented with stucco reliefs, which probably stands over the old substructions of the Villa Clodi.[137] On the side towards the lake there were open balconies for viewing the mock naval engagements; and near the entrance of the Barberini Villa the ruins of a theatre have been discovered. It appears probable from the numerous ruins found upon the edge of the lake that the whole of it was surrounded with quays and tiers of stone seats, and chapels of Nymphs, making it resemble a gigantic natural naumachia, or sheet of water for sham naval fights. These ruins may possibly, however, have belonged to separate private villas placed at different points round the water. To the south of Albano, in the grounds of the Villa Doria, there are the ruins of an extensive Roman villa. Whether this was a part of the Albanum Cæsarum or not, is uncertain. Some of the bricks bear the stamps of Domitian, others those of the third consulship of Servianus (A.D. 134), Hadrian’s brother-in-law, others of Commodus.[138] [Sidenote: Lago Albano or Di Castello.]