Portland Observatory

Portland Observatory
The Portland Observatory in 2024
Location138 Congress St
Portland, Maine
Coordinates43°39′55″N 70°14′54″W / 43.66528°N 70.24833°W / 43.66528; -70.24833
Arealess than one acre
Built1807
NRHP reference No.73000122
Significant dates
Added to NRHPApril 24, 1973
Designated NHLFebruary 17, 2006

The Portland Observatory is a historic maritime signal tower at 138 Congress Street in the Munjoy Hill section of Portland, Maine. Built in 1807, it is the only known surviving tower of its type in the United States. Using both a telescope and signal flags, two-way communication between ship and shore was possible several hours before an incoming vessel reached the docks. The tower was designated a National Historic Landmark and a National Historic Civil Engineering Landmark in 2006; it is now managed by Greater Portland Landmarks, a local historic preservation nonprofit. It is open to the public as a museum.