Stock Photo - Spain, Castilla-Leon, Ávila, The Walls of Ávila. Its main monument is the imposing Walls of Ávila (11th-14th centuries), begun in 1090. The enclosed area is 31 hectares (77 acres) with a perimeter of 2,516 metres (2,752 yd), 88 blocks of semicircular towers, 2,500 merlons, curtain walls 3 m (9 ft 10 in) thick, with an average height of 12 m (39 ft), and 9 gates. The Walls of Ávila is the largest fully illuminated monument in the world. It is possible to walk upon the walls themselves for roughly half their circumference. While some of the walls will never be navigable in this way because of their integration into other structures, a large stretch of the walls has yet to be made safe for pedestrians.