Captain Meriwether Lewis was commissioned by President Jefferson to explore the territories acquired by the 1803 Louisiana Purchase and to find ‘practicable water communication’ to the Pacific. Enlisting the soldier William Clark as his confederate, Lewis departed St Charles near St Louis with his ‘Corps of Discovery’ in May 1804, following the Missouri River. Passing through Sioux Territory, they built Fort Mandan in what is now North Dakota to overwinter. The following summer, they traversed the Rockies and, after almost starving on the Lolo Pass in Montana, reached the Pacific in November, spending their second winter at the mouth of the Columbia River, returning to St Louis in September, 1806. The explorers had been able to call on the prior cartography of Pond, Morse and Arrowsmith, and the ethnography of DuPratz (Lewis took a copy of his Histoire de Louisiane on the journey) but collected a wealth of original data.
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