Joshua 4:3-8

3and tell them to take up twelve stones from the middle of the Jordan, from right where the priests are standing, and carry them over with you and put them down at the place where you stay tonight.” 4So Joshua called together the twelve men he had appointed from the Israelites, one from each tribe, 5and 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, 6to serve as a sign among you. In the future, when your children ask you, ‘What do these stones mean?’ 7tell 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.” 8So the Israelites did as Joshua commanded them. They took twelve stones from the middle of the Jordan, according to the number of the tribes of the Israelites, as the Lord had told Joshua; and they carried them over with them to their camp, where they put them down.