Alcatraz Island later invalidated the sale and paid Frémont nothing. Frémont and his heirs sued for compensation during protracted but unsuccessful legal battles that extended into the 1890s. Following the acquisition of California by the United States as a result of the Treaty of Guadalupe Hidalgo (1848) which ended the Mexican–American War, and the onset of the California Gold Rush the following year, the U.S. Army began studying the suitability of Alcatraz Island for the positioning of coastal batteries to protect the approaches to San Francisco Bay. In 1853, under the direction of Zealous B. Tower, the United States Army Corps of
Alcatraz Citadel Grounds were located in the left centre. When the new concrete prison was built in 1910-2, iron staircases in the interior were retained from the old citadel and massive granite blocks originally used as gun mounts were reused as the wharf's bulkheads and retaining walls. Alcatraz Citadel Alcatraz Citadel, also known as Fort Alcatraz, was the original military defense and prison on Alcatraz Island, off the coast of San Francisco, California, United States. The citadel was built in 1859 as a U.S. Army military defense, and began function as a war camp in 1861 and long-term military prison in 1868.