Fort Wellington was built during the War of 1812 to defend the St. Lawrence River shipping route between Montreal and Kingston from possible attack by the United States. It was called into service again in 1838 when invasion from the United States was once more imminent. The fort continued to be used for military purposes, with occasional periods of abandonment, until it was transferred to the Department of the Interior in 1923 to be opened to the public as an historic site.