Main Prison Building

In 1907, the War Department drew up plans for a new prison building that could house up to 600 Army prisoners. When finished in 1912, the cellhouse was reportedly the largest steel-reinforced concrete building in the world. Unskilled Army inmates largely provided the labor. When Alcatraz was chosen as a federal maximum-security penitentiary in 1934, the aging cellhouse was renovated by the Bureau of Prisons. Tool-proof bars replaced the flat, mild-steel cell fronts of the military prison, gun galleries were built at either end of the cell room, and the number of cells was reduced from 600 to 336.

San Francisco, California · United States