The city walls of Canterbury are some of the most interesting and in places best preserved, of their kind in southern England. The whole of the medieval city wall was on the same line as the Roman city wall, built in the late third century. Structural remains of four Roman gates are known, the Worth Gate, the Riding Gate, the London Gate and the Queningate. All except the London Gate were re-used in medieval times. There are good grounds for supposing that Roman gates also preceded the medieval North Gate and West Gate, a seventh gate may have preceded the Burgate. Documentary evidence records the wall in 605 and 1011, when the Danes were "thrown from the wall", suggesting that they were then of a defensible height. Since the beginning of the twelfth century a stretch of wall, nineteen feet six inches high was incorporated in the nave of St Mary's Church. Repairs and building took place between 1153 and the late fifteenth century. Twenty- four medieval towers have now been identified. The city wall has disappeared over much of the area between the West Gate and Worth Gate.