Designated a National Historic Landmark in 1965 and a National Monument in 2001, Pompeys Pillar is nationally significant for the hundreds of historical markings, pictographs, petroglyphs, and inscriptions on its walls. These include the signature of Captain William Clark of the Lewis and Clark Expedition. On their return from the Pacific, Captains Meriwether Lewis and William Clark decided to split up to explore the country more thoroughly. Sacagawea and her eighteen-month-old son, Jean Baptiste Charbonneau (nicknamed “Pompey”), traveled with Clark. On July 26, 1806, Clark and his party arrived at this prominent rock formation, visible from the Yellowstone River. Clark stopped to climb the tower, which he named after young Jean Baptiste. He also etched his name and the date in the soft sandstone. His signature joined numerous petroglyphs—carved images of animals, shields, and other signs—created by American Indians who made their home here, including the Crow (Apsáalooke). One Apsáalooke name for this sacred site is Iishbíiammaache, “Where the Mountain Lion Lies.” Because the formation is a recognizable landmark located at a natural river crossing, the Apsáalooke often came here to hunt bison, trade with their allies, the Nez Perce and the Shoshones, and perform rituals. In 1805, French-Canadian fur trader Francois Antoine Larocque visited the site. On the sandstone tower he saw “sketched with red earth a battle between three people on horseback and three others on foot.” Later Euro-Americans also carved their names into the rock, including crew members of the steamboat Josephine in 1875 and infantrymen commanded by Colonel John Gibbon in 1876.