Fort Sumner was a coastal defense fortification on Munjoy Hill in Portland, Maine, United States.

It was reportedly originally named Fort Allen after the nearby Revolutionary War battery that probably became part of Fort Sumner, but was renamed in 1797 after Increase Sumner, the incumbent Governor of Massachusetts, of which Maine was then a part.

Fort Allen was rebuilt in 1814 with city resources, adding a magazine and barracks due to the British capture of Eastport and Castine in the War of 1812.

[6] Neal originally founded the gymnasium earlier that year at the Market House and moved it to Silver Street before finding a home at Fort Sumner.

Its main feature is the Fort Sumner Steps, which cross over the summit of Munjoy Hill.