In spite of pillage and wholesale destruction, there still exist numerous ancient monuments, of which the Pantheon of Agrippa is one of the most marvellous. The Vandals, who are usually charged with the work of destruction, pillaged the city, it is true, but they demolished nothing. The systematical destruction had begun long before their time, when the materials for building the first church of St. Peter were taken from the Circus of Caligula, and from other monuments near it. The same plan was pursued in the construction of innumerable other churches and buildings of every kind. Statues were broken to pieces and used for making lime, and in the beginning of the fifteenth century there only remained six of them in all Rome, five of marble and one of bronze. The invasion of the Normans in 1084, and the numerous wars of the Middle Ages, which were frequently attended by pillage and conflagrations, wrought further havoc, but so large had been the number of public buildings and monuments, that on the revival of art in the sixteenth century many still remained for study and imitation. Since that time the architectural collection enclosed by the walls of Rome has been guarded with the utmost care, and still further enriched by the masterpieces of Michael Angelo, Bramante, and others. On the Palatine Hill the most curious remains of ancient Rome, including the foundations of the palaces of the Cæsars and of the walls of _Roma Quadrata_, have recently been laid open. It was on this hill, so rich in precious relics, that the first Romans built their city, in order to afford it the protection of steep escarpments, and of the marshes on the Tiber and Velabro. When Rome grew more populous it became necessary to descend from this hill. The town spread over the valley of the Velabro, which had been drained by Tarquin the Etruscan, and then climbed up the surrounding hills. A small island in the Tiber occupied its centre. This the Romans looked upon as a sacred spot. They enclosed it by a masonry embankment, shaped like a ship, erected an obelisk in its centre to represent a mast, and a temple of Æsculapius upon the poop. This island was likened to a vessel bearing the fortunes of Rome.