The North West Company of Canada built a trading post here as Fort Nez Percés, and the Hudson's Bay Company rebuilt it as Fort Walla Walla in the early 1800's. In 1811, David Thompson of the Northwest Company led a fur trading party down the Columbia River, planted a British flag at the mouth of the Snake River, and claimed sovereignty over this region for Britain. Thompson and his party then met Walla Walla Chief Yellept at Wallula, where Thompson promised to build a trading post. In 1818, the North West Company built Fort Nez Percés at the mouth of the Walla Walla River, and after the HBC rebuilt it in 1821 it became known as Fort Walla Walla. The Wallula fort served as the Hudson's Bay Company center for outfitting and supplying all of the Company's inland empire fur brigades, as well as for trading with local tribes. The trading posts at Wallula stood on the north bank at the mouth of the Walla Walla River, a site now inundated by the backwaters of McNary Dam.