Deuteronomy 27:2-6

27:2 When you cross the Jordan River to the land the Lord your God is giving you, you must erect great stones and cover them with plaster. 27:3 Then you must inscribe on them all the words of this law when you cross over, so that you may enter the land the Lord your God is giving you, a land flowing with milk and honey just as the Lord, the God of your ancestors, said to you. 27:4 So when you cross the Jordan you must erect on Mount Ebal these stones about which I am commanding you today, and you must cover them with plaster. 27:5 Then you must build an altar there to the Lord your God, an altar of stones – do not use an iron tool on them. 27:6 You must build the altar of the Lord your God with whole stones and offer burnt offerings on it to the Lord your God.