What is the largest stone fort ever built in the United States?

Historic Fort Monroe, now a decommissioned military instillation in Hampton, Va., is the oldest, largest stone fort ever constructed in the United States and was once the two-year prison for Confederate States' president Jefferson Davis.

Fort Monroe was decommissioned on Sept. 15, 2011.

Located on Old Point Comfort on the southern tip of Virginia, the seven-sided star-shaped structure was built to guard the navigation channel between the Chesapeake Bay and Hampton Roads. That is the natural roadstead at the confluence of the Elizabeth, the Nansemond and the James rivers. Fort Wool, the sister of Fort Monroe, also sits there.

Fort Monroe covers 565 acres (Fort Wool 15 ac), with 3.2 miles of beachfront on the bay and 200 acres of natural resources.

In 1819, following the War of 1812 and the British burning of Washington D.C., President James Monroe devised a plan to build forts along coastal waterfronts to prevent foreign invaders from sailing into the country and repeating the British actions. Fort Monroe was completed in 1834. It was designed by French Napoleonic General of Engineers Simon Bernard.

On November 1, 2011, President Barack Obama signed a proclamation to designate portions of Fort Monroe as a National Monument.