The well-fortified hexagon sitting in the water of the Patapsco River just off the Key Bridge is Fort Carroll, an abandoned, pre-Civil War defense commissioned by Robert E. Lee himself that is so overgrown today that it acts as an informal bird sanctuary.
Fort Carroll was built in the late 1840s to defend the city of Baltimore from naval attacks, although like so many forts of its time this potential would never be realized. The manmade island base was designed as a concrete hexagon surrounding a central courtyard with large gun emplacements facing out towards the most assailable angle. The weaponry in the fort was reinforced during the Spanish-American war, but never used, and by the time World War I broke out, the fort and its guns were no longer relevant, thus the installation was officially abandoned in 1921 and stripped of its armaments.
The little geometric island sat dormant for decades, only being used briefly as a firing range during World War II. Finally in 1958 the fort was purchased by a Baltimore lawyer who proceeded to do nothing with it. As the years went by the fort became more and more overgrown as a small forest developed on the site and the concrete structure slowly cracked and fell apart.
With the new foliage and lack of any humans save for some intrepid urban explorers now and then, Fort Carroll has become home to a large population of seagulls and other birds. Today the island continues to sit unused save for some very lucky avian tenants.
Know Before You Go
The Fort is just east of the Francis Scott Key Bridge, in the middle of the shipping channel.