Arcos de la Frontera Castle was first constructed in the 11th century by the Moors when Arcos was briefly a taifa (small kingdom) before being captured by the Christians in 1250. The Christians rebuilt the castle as part of their campaign to retain their hold on the town, which was in a strategically important position for maintaining the border between the Muslim and Christian kingdoms.References:
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.