Joshua 8:2-4

2And you shall do to Ai and its king as you did to Jericho and its king, except that you may carry off their plunder and livestock for yourselves. Set up an ambush behind the city.”

3So Joshua and the whole army set out to attack Ai. Joshua chose 30,000 mighty men of valor and sent them out at night 4with these orders: “Pay attention. You are to lie in ambush behind the city, not too far from it. All of you must be ready.