Joshua 4:5-7

5and said to them, “Cross over before the ark of the LORD your God into the middle of the Jordan. Each of you is to take a stone upon his shoulder, according to the number of the tribes of Israel, 6to serve as a sign among you. In the future, when your children ask, ‘What do these stones mean to you?’ 7you are to tell them, ‘The waters of the Jordan were cut off before the ark of the covenant of the LORD. When it crossed the Jordan, the waters were cut off.’ Therefore these stones will be a memorial to the Israelites forever.”