the fort was built of cottonwood lumber cut from the riverbanks. it was triangular in shape, with high walls on all sides, an interior open space between structures, and a gate facing the missouri river, by which the party would normally travel. storage rooms provided a safe place to keep supplies. lewis and clark shared a room. the men of the corps of discovery started the fort on november 2, 1804. they wintered there until april 6, 1805. according to the journals, they built the fort slightly downriver from the five villages of the mandan and hidatsa nations.