Deuteronomy 4:41-43

Then Moses set apart three cities in the east beyond the Jordan, that the manslayer might flee there, anyone who kills his neighbor unintentionally, without being at enmity with him in time past; he may flee to one of these cities and save his life: Bezer in the wilderness on the tableland for the Reubenites, Ramoth in Gilead for the Gadites, and Golan in Bashan for the Manassites.