Doubtlessly coins have a special importance in characterizing and knowing some matters which have relationship with the time in which the coins were made in. They are considered official documents that couldnt be distorted. The error in the coins is very rare. Coins are the main resource if the sources are limited. The importance is not according the purity of the metal or the weights , moreover , the importance is in the writings and pictures inscripted on. So we know the history and the place of manufacture and occasionally the name of the person who commanded the operation of making the coins and the limits of his religious and living authority and some other features of live he was living.