From 1804 to 1806, Captains Meriwether Lewis and William Clark led about 40 soldiers and boatmen on an expedition commissioned by President Thomas Jefferson to find a route to the Pacific Ocean through the newly acquired Louisiana territory. This Corps of Discovery mapped the land, recorded its resources, and contacted its native inhabitants as it crossed a landscape that has since been altered by dams, logging, plowing, and roads. The United States had purchased the Louisiana territory, more than 830,000 square miles, from France in 1803. Jefferson chose Lewis to lead the expedition, and with Jefferson's permission Lewis asked William Clark to serve as co-leader; though opposite in temperament, they worked harmoniously throughout the two-year journey. Lewis left Washington, D.C., on July 5, 1803, acquired arms from Harpers Ferry arsenal on July 8, gathered supplies in Pittsburgh during July and August, and was joined by Clark in Louisville, Kentucky, in October. After wintering at Camp Wood in 1803 to 1804, the expedition left on May 14, 1804. It held a first council with Indians on August 3, 1804; Sgt. Floyd died on August 20; and from September 25 to 28 it was confronted by Teton Sioux Indians. After building Fort Mandan for winter quarters in 1804 to 1805, the party first arrived at Great Falls of the Missouri on June 13, 1805, purchased horses from Shoshoni Indians on August 30, and built canoes with help from Nez Perce Indians from September 26 to October 7, 1805. It reached the mouth of the Columbia River on November 15, 1805, built Fort Clatsop for winter quarters in 1805 to 1806, started the return trip on March 23, 1806, split on July 3, clashed with Blackfeet Indians on July 27, and after Lewis was accidentally shot on August 11 and the two leaders rejoined on August 12, arrived in St. Louis on September 23, 1806.