Joshua set up twelve stones in the midst of the Jordan, in the place where the feet of the priests who bore the ark of the covenant stood: and they are there to this day.
The immense importance of the ark of the covenant also shines in passages such as this.  And where, pray tell, did this ark of the covenant come from?  It is starkly clear to every student of the Bible that Joshua is but a continuation of the historical books called the Pentateuch.  If one wishes to know all about the ark of the covenant, he may surely read it in the Five Books of Moses, and it is no wonder that Moses' successor was the official custodian of that ark and all that it represented.