Fort Lennox was the third fortification built on Isle-aux-Noix as a barrier to invasion along the Richelieu River from the south. The island was first fortified by the French in 1759, but the British captured it the next year. In 1775 the Americans occupied the island as a base for their attack on Canada. After they retreated, the British erected a new fort to deter further American invasion. During the War of 1812 it protected an important naval base. Later this fort was razed, and a new masonry work, Fort Lennox, was built from 1819 to 1829 to guard the Canadian border. It was garrisoned until 1870.
