Fort Knox

Fort Knox sits on the west bank of the Penobscot River in Prospect, Maine, about 5 miles from the river's mouth. It was built between 1844 and 1869 and was the first fort in Maine made entirely of granite, when most earlier forts used wood, earth and stone. It is named for Major General Henry Knox, the first U.S. Secretary of War, who lived his last years in nearby Thomaston.

It is a nearly intact example of a mid-19th century granite coastal fortification, listed on the National Register of Historic Places in 1969 and declared a National Historic Landmark in 1970. The fort is also the entry point to the observation tower of the Penobscot Narrows Bridge.

In eastern Maine, memory of defeats at British hands during the Revolution and the War of 1812 fed a lasting distrust. The Penobscot Expedition of 1779 ended in disaster, and in 1814 the British sailed up the river and won the Battle of Hampden. After the Aroostook War of 1838–1839 renewed those fears, and with the Penobscot valley a major source of shipbuilding timber, the river was added to the Third System of coastal fortifications. Construction began in 1844. Congress funded it only in fits and starts, and masonry funding ended in 1869 with the design never fully completed.

Joseph G. Totten, the Army Corps of Engineers' leading fortification engineer, designed it, and the granite was quarried upriver at Mount Waldo in Frankfort. The main fort had 64 guns, plus two water batteries with furnaces to heat cannonballs. Fort Knox never saw battle, though it was manned during the Civil War by volunteers in training and during the Spanish–American War by a Connecticut regiment. In 1900 a storehouse for naval mines was built there, and it is now the visitor center. Maine bought the fort in 1923, and it has been a state historic site since 1943.