TSK · Numbers 32:17

Moses said to them:“If the Gadites and the Reubenites cross the Jordan with you, each one equipped for battle in the LORD’s presence, and you conquer the land, then you must allot them the territory of Gilead as their possession.

The Reubenites, Gadites, and the half-tribe of Manasseh crossed over armed for battle ahead of the Israelites, just as Moses had instructed them.