Joshua 4
7 Ref Then you will say to them, Because the waters of Jordan were cut off before the ark of the Lord's agreement; when it went over Jordan the waters of Jordan were cut off: and these stones will be a sign for the children of Israel, keeping it in their memory for ever.
8 Ref So the children of Israel did as Joshua gave them orders, and took twelve stones from the middle of Jordan, as the Lord had said to Joshua, one for every tribe of the children of Israel; these they took across with them to their night's resting-place and put them down there.