Deuteronomy 4:41-43

Then Moses set apart three cities beyond the Jordan toward the sunrising; that the manslayer might flee thither, that slayeth his neighbor unawares, and hated him not in time past; and that fleeing unto one of these cities he might live: namely, Bezer in the wilderness, in the plain country, for the Reubenites; and Ramoth in Gilead, for the Gadites; and Golan in Bashan, for the Manassites.