And Moses said unto them, If the children of Gad and the children of Reuben will pass with you over Jordan, every man armed to battle, before the Lord, and the land shall be subdued before you; then ye shall give them the land of Gilead for a possession: (Numbers 32:29)
The whole of Gilead was scarcely in their possession at this point. They were fortifying a number of cities, not only as safe refuges for their families, but also as strong points from which to complete subjection of the land.