Fort Mandan was the name of the encampment at which the Lewis and Clark Expedition wintered in 1804- 1805. The encampment was located on the Missouri River approximately twelve miles from Washburn, North Dakota, though the precise location is not known for certain and may be under the nearby river. The fort was built of cottonwood lumber cut from the riverbanks. It was triangular in shape, with high walls on all sides and a gate facing the riverbank. The Corps of Discovery started the fort on November 2, 1804, and remained in the area until April 7, 1805. They built the fort slightly down river from the nearby Mandan tribe's village. The Mandan were a tribe that Lewis was specifically told to trade with by then President Thomas Jefferson. During the Corps' stay at the Fort, the Sioux threatened to attack the Mandan village along with the explorers. Although several small parties of Sioux did attack, no major conflict arose. Also, the winter was very cold with temperatures sometimes dipping to minus 45 degrees Fahrenheit and quite a few men of the expedition were frost-bitten. When the Corps passed back through the area in August 1806 on their return journey home, the fort had burnt to the ground; the reason is unknown. Since that time, the Missouri River has slowly eroded its bank and has shifted to the east, covering up what remained of the charred fort. A replica stands along the river, 2.5 miles from the intersection of ND 200A and US 83. It is located near the North Dakota Lewis and Clark Interpretive Center.