Joshua 4:5-9

and Joshua said to them, “Cross again to the ark of the LORD your God into the middle of the Jordan, and each of you take up a stone on his shoulder, according to the number of the tribes of the sons of Israel. Let this be a sign among you, so that when your children ask later, saying, ‘What do these stones mean to you?’ then you shall say to them, ‘Because the waters of the Jordan were cut off before the ark of the covenant of the LORD; when it crossed the Jordan, the waters of the Jordan were cut off.’ So these stones shall become a memorial to the sons of Israel forever.” Thus the sons of Israel did as Joshua commanded, and took up twelve stones from the middle of the Jordan, just as the LORD spoke to Joshua, according to the number of the tribes of the sons of Israel; and they carried them over with them to the lodging place and put them down there. Then Joshua set up twelve stones in the middle of the Jordan at the place where the feet of the priests who carried the ark of the covenant were standing, and they are there to this day.