Some type of fortification or gun emplacement located outside the actual fort but still on its grounds.

*****

Fort Washington, located in Maryland, was for many decades the only defensive fort protecting Washington, D.C. The original fort, overlooking the Potomac River, was completed in 1809, and was begun as Fort Warburton but renamed in 1808. During the War of 1812 the fort was destroyed by its own garrison during a British advance.

The current historic fort -- maintained by the National Park Service -- was initially constructed in 1824.

Survivor, posted earlier