In 1775, the island was named La Isla de los Alcatraces (Island of the Pelicans) by a Spanish explorer, Juan Manuel de Ayala. In 1850 American President Millard Fillmore reserved the island that is located in the San Francisco Bay (about 1.5 miles from San Francisco) for military use. A fortress with 100 cannons was built to protect the San Francisco Bay as was the first operational lighthouse on the west coast. The island was also used by the military as a prison. In the early 1900s, the military inmates built the 600 cell-structure that still stands to this day. Construction was completed around 1912.