The Crow (or Absaroke) were originally part of the Hidatsa, a Siouan people who lived a settled, agricultural life along the Missouri River in what is now western North Dakota. Some time prior to the mid-17th century, the Hidatsa leader No-Vitals led a large number of Hidatsa west into the Yellowstone River valley of south-central Montana, where the tribe lived on the plains, by the river, and in the nearby Big Horn, Pryor, and Wolf Mountains. On the move due to pressure from eastern and midwestern tribes moving west due to white encroachment, the Crow may have settled in the Yellowstone Valley only a few decades before the arrival of Lewis and Clark. A fundamental tenet of Crow religion was maxpe, or the sacred.