Deuteronomy 27:4-7

When you cross the Jordan, set up these stones at Mount Ebal and coat them with plaster, as I am commanding you today. “Then build an altar there to the LORD your God, using natural, uncut stones. You must not shape the stones with an iron tool. Build the altar of uncut stones, and use it to offer burnt offerings to the LORD your God. Also sacrifice peace offerings on it, and celebrate by feasting there before the LORD your God.