Joshua 4:20-23

It was there at Gilgal that Joshua piled up the twelve stones taken from the Jordan River. Then Joshua said to the Israelites, “In the future your children will ask, ‘What do these stones mean?’ Then you can tell them, ‘This is where the Israelites crossed the Jordan on dry ground.’ For the LORD your God dried up the river right before your eyes, and he kept it dry until you were all across, just as he did at the Red Sea when he dried it up until we had all crossed over.