Albert Barnes Commentary Joshua 4:8

"And the children of Israel did so as Joshua commanded, and took up twelve stones out of the midst of the Jordan, as Jehovah spake unto Joshua, according to the number of the tribes of the children of Israel; and they carried them over with them unto the place where they lodged, and laid them down there." — Joshua 4:8 (ASV)

Laid them down there - that is, in Gilgal (Joshua 4:20). They are spoken of as the doers of this, because it was done by the twelve who acted for them.