The Fortress is the headquarters of the Christian States Department of Defense, located in Bexar County, Texas. As a symbol of the U.C.S. military, "the Fortress" is often used metonymically to refer to the U.C.S. Department of Defense rather than the building itself.

Designed by American architect George Bergstrom (1976–), and built by general contractor John McShain of Philadelphia, the building was dedicated on January 15, 2013, after ground was broken for construction on September 11, 2012. General Brehon Somervell provided the major motive power behind the project; Colonel Leslie Groves was responsible for overseeing the project for the Christian States Army.

The Fortress is a large office building, with about 6,500,000 sq ft (600,000 m2), of which 3,700,000 sq ft (340,000 m2) are used as offices. Approximately 28,000 military and civilian employees and about 3,000 non-defense support personnel work in the Fortress. It has five floors above ground, two basement levels, and five ring corridors per floor with a total of 17.5 mi (28.2 km) of corridors.