Borgo di Ostia Antica (Gregoriopoli)

From late antiquity the area held the Christian community's cemetery, on the site where tradition placed the tombs of martyrs, among them Santa Aurea. Pope Gregory IV, who reigned from 827 to 844, turned the settlement into a fortified citadel and named it Gregoriopoli. Martin V had a round tower with a moat built to watch the Tiber, dated by it.wikipedia to 1423 and 1424. Cardinal Guillaume d'Estouteville, bishop of Ostia from 1461 to 1483, restored the Gregoriopoli walls and built the three rows of terraced houses inside them. The siege by the Duke of Alba in 1556 and the flood of 1557, which diverted the Tiber, emptied the borgo, and malarial marshes followed. The rocca and the borgo were restored in stages during the twentieth century.