Joshua 4:5-9

and Joshua said unto them, Pass over before the ark of Jehovah your God into the midst of the Jordan, and take you up every man of you a stone upon his shoulder, according unto the number of the tribes of the children of Israel; that this may be a sign among you, that, when your children ask in time to come, saying, What mean ye by these stones? then ye shall say unto them, Because the waters of the Jordan were cut off before the ark of the covenant of Jehovah; when it passed over the Jordan, the waters of the Jordan were cut off: and these stones shall be for a memorial unto the children of Israel for ever. 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. And Joshua set up twelve stones in the midst of the Jordan, in the place where the feet of the priests that bare the ark of the covenant stood: and they are there unto this day.