Flavius Josephus, Antiquities of the Jews
William Whiston, A.M., Ed.

[172] Moses also now built those ten cities which were to be of the number of the forty-eight [for the Levites;]; three of which he allotted to those that slew any person involuntarily, and fled to them; and he assigned the same time for their banishment with that of the life of that high priest under whom the slaughter and flight happened; after which death of the high priest he permitted the slayer to return home. During the time of his exile, the relations of him that was slain may, by this law, kill the manslayer, if they caught him without the bounds of the city to which he fled, though this permission was not granted to any other person. Now the cities which were set apart for this flight were these: Bezer, at the borders of Arabia; Ramoth, of the land of Gilead; and Golan, in the land of Bashan. There were to be also, by Moses's command, three other cities allotted for the habitation of these fugitives out of the cities of the Levites, but not till after they should be in possession of the land of Canaan.