Joshua 4:5-9

and said to them, “Go out into the river where the Ark of the LORD your God is. Each of you bring back one rock, one for each tribe of Israel, and carry it on your shoulder. They will be a sign among you. In the future your children will ask you, ‘What do these rocks mean?’ Tell them the water stopped flowing in the Jordan when the Ark of the Agreement with the LORD crossed the river. These rocks will always remind the Israelites of this.” So the Israelites obeyed Joshua and carried twelve rocks from the middle of the Jordan River, one rock for each of the twelve tribes of Israel, just as the LORD had commanded Joshua. They carried the rocks with them and put them down where they made their camp. Joshua also put twelve rocks in the middle of the Jordan River where the priests had stood while carrying the Ark of the Agreement. These rocks are still there today.