Alcatraz began as a U.S. Army fort designed to defend San Francisco Bay against enemy attack. At the height of the Civil War, the fortified island held over 100 heavy cannon, including sleek Rodman guns on iron carriages. The Rodmans’ distinctive soda bottle shape reflected the pressures that built up inside the barrel during firing. Nicknamed after their inventor, Thomas Jackson Rodman, the guns’ design and careful manufacture made them very safe weapons to fire at a time when many cannon blew up without warning. Rodmans ranged in size from 8-inch caliber guns up through 15-inch caliber models that weighed nearly 50,000 pounds.