Joshua 4:8-9

So the men did as Joshua had commanded them. They took twelve stones from the middle of the Jordan River, one for each tribe, just as the LORD had told Joshua. They carried them to the place where they camped for the night and constructed the memorial there. Joshua also set up another pile of twelve stones in the middle of the Jordan, at the place where the priests who carried the Ark of the Covenant were standing. And they are there to this day.