Joshua 8:1-3 (NKJV)
¹  Now the LORD said to Joshua: “Do not be afraid, nor be dismayed; take all the people of war with you, and arise, go up to Ai. See, I have given into your hand the king of Ai, his people, his city, and his land.
²  And you shall do to Ai and its king as you did to Jericho and its king. Only its spoil and its cattle you shall take as booty for yourselves. Lay an ambush for the city behind it.”
³  So Joshua arose, and all the people of war, to go up against Ai; and Joshua chose thirty thousand mighty men of valor and sent them away by night.