Cagliari is built on seven hills and it is thought that the Romans worshipped the god Aesculapius atop the Colle di San Michele. In the Byzantine era, the pagan worship for the protector of medicine was replaced by the Christian worship for San Michele. Perhaps it is no coincidence that on the top of the hill, which can be reached from hairpin bends rising up between white tuffaceous rocks and the green of agaves and Mediterranean greenery, it appears there was once a monastery and, later, a church dedicated to the archangel. Rising up today, in excellent condition, is a medieval castle that overlooks the city, surrounded by a green park. Once isolated, today it is part of the is Mirrionis district. A 360-degree view of the capital can be enjoyed from the top, with the Pisan towers of the Castello district, the port, the Poetto, the Sella del Diavolo and the Santa Gilla lagoon. The manor, having long been the sentinel of the access road from Campidano, can be seen from all points around the town and the surrounds, even from kilometres away.