On Thursday, June 13, 1805, Captain Meriwether Lewis reached the Great Falls of the Missouri River, after Mandan Indian chiefs had told the Corps of Discovery the previous winter that the party would encounter falls on the river. Lewis found not only the Great Falls but four more falls upstream, and for the next three weeks the men portaged their boats and equipment eighteen miles overland around the falls. This portage was the most grueling stretch of the journey the expedition had faced so far.