The half-tribe of Manasseh asked for the same land as the tribes of Reuben and Gad. Moses accepted their request (see 3:12). Gad and Reuben settled between the Arnon River and the middle of Gilead (see 2:24; 2:36). Manasseh captured the land north of that, including Bashan (see 3:1).
The Rephaites were a giant people related to the Anakites (see 2:11). This passage notes that they were native to Bashan.