Joshua 4:4-7

So Joshua called together the twelve men he had appointed from the Israelites, one from each tribe, and said to them, “Go over before the ark of the LORD your God into the middle of the Jordan. Each of you is to take up a stone on his shoulder, according to the number of the tribes of the Israelites, to serve as a sign among you. In the future, when your children ask you, ‘What do these stones mean?’ tell them that the flow of the Jordan was cut off before the ark of the covenant of the LORD. When it crossed the Jordan, the waters of the Jordan were cut off. These stones are to be a memorial to the people of Israel forever.”