In the summer of 1837, the steamboat St. Peters arrived at the Mandan village and Fort Clark carrying passengers, supplies, and trade goods, but some aboard were infected with smallpox. Within weeks, the epidemic decimated the Mandans, leaving fewer than 160 survivors from an estimated population of 1600. Most of the survivors left Mih-tutta-hang-kush and, with others, moved farther north. In the spring of 1838, neighboring Arikaras moved into the village. The village core had previously served as a central plaza, an important feature of Mandan villages, where the Ark of the First Man stood in the middle of the open space as a barrel-shaped object representing the height of waters in a great flood and playing an important role in Mandan ceremonies. Around the plaza stood the homes of some of the tribe's most prominent members as well as the Mandan ceremonial lodge. After the Arikaras arrived, they built their own ceremonial lodge over the place where the Mandan Ark of the First Man had been located.