Fort St. Pierre
The first post on Rainy Lake was Fort Tekamanigan, built by Robutel de La Noue in 1717, but soon abandoned, probably because of Sioux hostility. In 1731, Sieur de La Jemaraye, La Vérendrye's nephew and lieutenant, constructed Fort St. Pierre at the south-west end of the lake where it drains into the Rainy River. As one of the postes de la Mer de l 'Ouest it served as a trading post and base for La Vérendrye 's westward explorations. Fort St. Pierre was abandoned by the French about 1758 during the course of the Seven Years' War.
Plaque via Alan L. Brown's site Ontario Plaques. Full page here.