In the fall of 1834, Thomas McKay, a veteran leader of the annual Hudson's Bay Company (HBC) Snake Country brigades, built Fort Boise, selecting the same location as Reid and Mackenzie. Although McKay had retired in 1833, the HBC Chief Factor John McLoughlin sent him to establish Fort Boise in 1834 to challenge the newly built American Fort Hall further east on the Snake River.
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.