On September 23, 1806, the Lewis and Clark Expedition (formally the Corps of Discovery Expedition) returned to St. Louis after two and a half years, having gathered information about the northwestern region of the Louisiana Purchase between the Mississippi and the Pacific, and laying claim to the Oregon Territory. Its objectives were to map the uncharted continent and study flora, fauna and resources to be exploited economically. President Jefferson also placed special importance on showing U.S. dominance over Native Americans along the Missouri River. Pictured: one of many “Indian Peace Medals” carried by Lewis and Clark, intended to establish U.S. sovereignty over indigenous inhabitants. It is actually two silver plates held within a silver ring; the U.S. Mint could not yet strike solid, heavy medals.