Deuteronomy 4:41-43

411Then Moses set apart three cities across the Jordan to the 2east, 42that a manslayer might flee there, who unintentionally slew his neighbor without having enmity toward him in time past; and by fleeing to one of these cities he might live: 433Bezer in the wilderness on the plateau for the Reubenites, and Ramoth in Gilead for the Gadites, and Golan in Bashan for the Manassites.