This sacred spot, and the church built to commemorate it, were naturally the centre of all those religious traditions which separate Rome from every other city. It was to preserve them from assault, "in order that it should be less easy for the enemy to make depredations and burn the Church of St. Peter, as they have heretofore done," that Leo IV, the first pope whom we find engaged in any real work of construction, built a wall round the mound of the Vatican, and Colle Vaticano--"little hill," not so high as the seven hills of Rome--where against the strong wall of Nero's Circus Constantine had built his great basilica. At that period--in the middle of the ninth century--there was nothing but the church and shrine--no palace and no hospital. The existing houses were given to the Corsi, a family which had been driven out of their island, according to Platina, by the Saracens, who shortly before had made an incursion up to the very walls of Rome, whither the peoples of the coast (_luoghi maritimi del Mar Terreno_) from Naples northward had apparently pursued the corsairs, and helped the Romans to beat them back. One other humble building of some sort, "called Burgus Saxonum, Vicus Saxonum, Schola Saxonum, and simply Saxia or Sassia," it is interesting to know, existed close to the sacred centre of the place, a lodging built for himself by Ina, King of Wessex, in 727. Thus the English have a national association of their own with the central shrine of Christianity. There was also a Schola Francorum in the Borgo. The pilgrims must have built their huts and set up some sort of little oratory--favored, as was the case even in Pope Nicholas' day, by the excellent quarry of the Circus close at hand--as near as possible to the great shrine and basilica which they had come so far to say their prayers in, and attracted, too, no doubt, by the freedom of the lonely suburb between the green hill and the flowing river. Leo IV built his wall round this little city, and fortified it by towers. "In every part he put sculptors of marble and wrote a prayer," says Platina. One of these gates led to St. Pellegrino, another was close to the castle of St. Angelo, and was "the gate by which one goes forth to the open country." The third led to the School of the Saxons; and over each was a prayer inscribed. These three prayers were all to the same effect--"that God would defend this new city which the Pope had enclosed with walls and called by his own name, the Leonine City, from all assaults of the enemy, either by fraud or by force."