Begun on orders of Alfonso VI as part of the general reconquest of Spain from the Moors, the 11th-century Walls of Avila, built over Roman fortifications, took 9 years to complete. They average 10m (33 ft.) in height and have 88 semicircular towers and more than 2,300 battlements. Of the nine gateways, the two most famous are the St. Vincent and the Alcázar, both on the eastern side. In many respects, the walls are best viewed from the west. Whatever your preferred point of view, you can drive along their entire length: 2km (1 1/2 miles).