Deuteronomy 13:15-17

you shall most certainly strike the inhabitants of that city with the edge of the sword, utterly destroying it and all that is in it, even its livestock with the edge of the sword. Then you shall collect all its spoil (plunder) into the middle of its open square and burn the city and set fire to the spoil as a whole burnt offering to the LORD your God. It shall be a ruin forever. It shall not be built again. Nothing from that which is put under the ban (designated for destruction) shall cling to your hand, so that the LORD may turn away from His burning anger and show mercy to you, and have compassion on you and make you increase, just as He swore to your fathers