Joshua 4:4-6

So Joshua sent for the twelve men, whom he had ready, one man out of every tribe of the children of Israel, And he said to them, Go over before the ark of the Lord your God into the middle of Jordan, and let every one of you take up a stone on his back, one for every tribe of the children of Israel: So that this may be a sign among you; when your children say to you in time to come, What is the reason for these stones?