Deuteronomy 13:15-17

you must strike down the inhabitants of that city with the sword. Completely destroy everyone in it as well as its livestock with the sword. You are to gather all its spoil in the middle of the city square and completely burn the city and all its spoil for the LORD your God. The city is to remain a mound of ruins forever;  it is not to be rebuilt. Nothing set apart for destruction is to remain in your hand, so that the LORD will turn from his burning anger and grant you mercy, show you compassion, and multiply you as he swore to your ancestors.