The town center is completely enclosed by the old town walls, built by the Romans in the second and third centuries A.D. and renovated or rebuilt in the 14th century. They have a total length of 2,131m/2,330yd, an average height of 11m/36ft and an average thickness of 4.5m/15ft. Of the original total of 85 towers 50 have survived the various sieges of the town. There are ten gates, the oldest of which are the Puerta de Miñá, Puerta de Falsa and Puerta de Nova. The Puerta de Santiago, opposite the cathedral, was built in the 18th century and is surmounted by a figure of Santiago Matamoros, St James as the Moor-Slayer. At the gates there are steps up to the wall-walk, and a walk round it, which takes about half an hour, affords interesting glimpses of the town, including its back yards, and views of the surrounding hills.