Joshua 8:11-13

11And all the people of war who were with him went up and drew near; and they came before the city and camped on the north side of Ai. Now a valley lay between them and Ai.

12So he took about five thousand men and set them in ambush between Bethel and Ai, on the west side of the city.

13And when they had set the people, all the army that was on the north of the city, and its rear guard on the west of the city, Joshua went that night into the midst of the valley.