In November 1803, Meriwether Lewis, William Clark, and their growing Corps of Discovery contingent spent five days here teaching one another celestial navigation and surveying skills. Using a sextant, octant, artificial horizon, and reference tables, they successfully obtained the first longitude and latitude data they would use during the Expedition. Subsequent maps of the northern and western portions of the United States, prepared using Lewis and Clark's data, began at the confluence of these great rivers, which in 1803 was located just south of 2nd Street in present-day Cairo.