The children of Israel did so as Joshua commanded, and took up twelve stones out of the midst of the Jordan, as Yahweh spoke to Joshua, according to the number of the tribes of the children of Israel; and they carried them over with them to the place where they lodged, and laid them down there.
Some scholars have squirmed and quibbled over the setting up of two memorials, as mentioned here, declaiming on the stupidity of setting up a memorial where nobody would see it at the bottom of the Jordan, and other choice bits of human cavil.  Well, we thank God for the discernment of one like Pink, who has this: