The city walls around Canterbury are some of the best preserved, in places, of their kind in southern England. The medieval city wall was on the same line as the Roman city wall, built in the late third Century, and is a sequence of defensive walls around the city. 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. Since the beginning of the 12th Century, a stretch of wall, nineteen feet six inches high was incorporated in the nave of St Mary's Church. Building and repairs took place between 1153 and the late 15th Century. Like many parts of this medieval city, you come across historic sites and you can see parts of the wall as you walk around, including by Dane John Gardens.