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. Geography Portland has a deep harbor sheltered by numerous islands. Ships entering the harbor are not directly visible from the wharfs, which created problems for merchants trying to prepare for the arrival of cargoes. This problem was solved in 1807 when Captain Lemuel Moody organized the construction of an observatory on Portland's Munjoy Hill, visible from both the open ocean and the wharfs. During the War of 1812, the observatory was used as a watch tower. About the observatory The 86-foot (26 m) tall observatory (7 stories) is octagonal (to lessen wind pressure on each side) and lighthouse-shaped, with a fieldstone base of heavy loose rocks, and stands 222 feet (68 m) above sea level. There is no basement but the rock ballast in the bottom floor and octagonal design have kept the structure steady during storms. The observatory's 'lantern' (cupola) included a P & J Dollond Achromatic Refracting Telescope, which could identify ships 30 miles (48 km) to sea. That telescope disappeared from the observatory in 1939. The observatory has been renovated numerous times over the years, including a Works Progress Administration renovation in 1939. It was most recently renovated from 1998-2000 to repair damage from moisture and powderpost beetles. This renovation won a 2001 National Preservation Honor Award from the National Trust for Historic Preservation. The center column was not an original feature, and was added in the 1939 renovation. In 2014 additional repairs to the windows and shingles were underway. The observatory was placed on the National Register of Historic Places in 1972. In 2006, the observatory was made a National Historic Landmark and a National Historic Civil Engineering Landmark. Past operation The Portland Observatory is the only remaining maritime signal station in the United States. Tower operations were paid with annual fees collected from shipping