Called Iishiia Anaache, or "Place Where the Mountain Lion Dwells," by the Apsaalooka (Crow) people, Pompey's Pillar was a well-known landmark to the Plains Indians. At this strategic natural crossing of the Yellowstone, or Elk River as it was known to the Apsaalooka, Indian people met to trade and exchange information. They painted pictographs and etched petroglyphs onto the sheer cliffs. Apsaalooka legend reports that Pompey's Pillar was once attached to the sandstone bluffs on the north side of the river, but the rock later detached itself from the cliffs and rolled across the river to its present site. Pompey's Pillar also became a significant landmark for Euro-American explorers, fur trappers, soldiers, and immigrants. It was discovered by Canadian North West Company employee Francois Larocque in 1805. A little less than a year later, on July 25, 1806, a 12 man detachment under the command of William Clark, including Sacajawea and her infant son, visited it. Clark carved his name and the date on the rock and named it in honor of Sacajawea's son. He was one of hundreds of individuals who for generations left their marks on the rock.