Fort Mifflin on a tidal island in the Delaware River

Fort Mifflin sits on a tidal island (Mud Island) along the Delaware River and defended Philadelphia's river approaches during the Revolutionary War, including the 1777 siege. The fort's location is physically separated by tidal channels and marshland from much of the city, making it a notable island-like geographic feature within Philadelphia's river corridor. The site survives as a historic fortification and landmark on the river's edge.