The University of Dayton (UD) is an American private Roman Catholic national research university in Ohio's sixth-largest city, Dayton. Founded in 1850 by the Society of Mary (Marianists), it is one of three Marianist universities in the nation and the largest private university in Ohio. The university's campus is located in the city's southern portion and spans 388 acres on both sides of the Great Miami River. The campus is noted for the Immaculate Conception Chapel and the University of Dayton Arena.