Lewis, given his choice of associate, selected William Clark, who was appointed by Jefferson second lieutenant of artillery. Clark was a brother of George Rogers Clark, by whose valor and sagacity the Illinois or Northwest Territory was secured to the United States, and this connection made his selection for further extension of the country seem most fitting. Moreover young Clark had qualifications and experiences which strongly commended him to Lewis. Born in Virginia, August 1, 1770, William Clark had a thorough knowledge of the privations and conditions of frontier life. Skilful as a hunter, a keen observer, familiar with military life from four years of service as a lieutenant of infantry, and developed from his ill health, which caused him to leave the army in 1796, into a magnificent specimen of manhood, he proved so efficient a coadjutor that his name will ever be inseparably associated with that of Lewis. Lewis left Washington July 5, 1803, his mission being enhanced in its importance by the formal cession of Louisiana to the United States by the treaty of Paris, April 30, 1803, which news reached him July 1st. The rendezvous was at St. Louis, which was reached via Pittsburgh and the Ohio, recruits being selected at various posts, while Lieutenant Clark joined at Louisville, though he was not commissioned in the army till the following March. When the party reached St. Louis, in December, 1803, formal notice of the transfer of Louisiana had not reached the Spanish commandant, who would not permit their passage westward. They passed the winter in camp opposite the mouth of the Missouri, where they built a barge with sail-power and two smaller boats, with which they started up the Missouri River on May 14, 1804. The expedition, commanded by Captain Lewis, with Lieutenant Clark as second, comprised thirty-four selected men, eleven being watermen, a negro servant, and a hunter, who was also an interpreter.