Joshua 4:8-9

8So Bnei-Yisrael did so, as Joshua commanded. They lifted twelve stones from the middle of the Jordan, just as Adonai had said to Joshua, for the number of the tribes of Bnei-Yisrael. Then they carried them over with them to the lodging place and put them down there.

9Joshua also set up twelve stones in the middle of the Jordan, at the spot where the feet of the kohanim carrying the ark of the covenant were standing—they are there to this day.