The peak of Santa Lucia del Mela was an important military outpost. On the remains of the former city walls the Byzantines built a fort, subsequently rebuilt by the Arabs between 837 and 851. Frederick II of Aragon fortified the town with walls and renovated its castle. The castle was left to decay in the 17th century, but has been restored later.
The city walls of Avila were built in the 11th century to protect the citizens from the Moors. They have been well maintained throughout the centuries and are now a major tourist attraction as well as a UNESCO World Heritage Site. Visitors can walk around about half of the length of the walls.
The layout of the city is an even quadrilateral with a perimeter of 2,516 m. Its walls, which consist in part of stones already used in earlier constructions, have an average thickness of 3 m. Access to the city is afforded by nine gates of different periods; twin 20 m high towers, linked by a semi-circular arch, flank the oldest ones, Puerta de San Vicente and Puerta del Alcázar.