Joshua 3:4

Yet there shall be a space between you and it, about two thousand cubits by measure (three thousand feet). Come not near unto it, they were to observe this respectful distance, lest their vanguard hide the Ark of the Covenant from the great number of the marchers, that ye may know the way by which ye must go; for ye have not passed this way heretofore. It was not that the people were in danger of losing their way to the river, but that the Lord wanted them to note the miracle by which He opened the way to Canaan before their eyes.