Joshua 4:5-9

and Joshua said to them: “Cross over before the ark of the LORD your God into the midst of the Jordan, and each one of you take up a stone on his shoulder, according to the number of the tribes of the children of Israel, that this may be a sign among you when your children ask in time to come, saying, ‘What do these stones mean to you?’ Then you shall answer them that the waters of the Jordan were cut off before the ark of the covenant of the LORD; when it crossed over the Jordan, the waters of the Jordan were cut off. And these stones shall be for a memorial to the children of Israel forever.” And the children of Israel did so, just as Joshua commanded, and took up twelve stones from the midst of the Jordan, as the LORD had spoken to Joshua, according to the number of the tribes of the children of Israel, and carried them over with them to the place where they lodged, and laid them down there. Then Joshua set up twelve stones in the midst of the Jordan, in the place where the feet of the priests who bore the ark of the covenant stood; and they are there to this day.