But it was not only legal documents that were attested by the signet; letters also were sealed up by the sender before they left his hands,[18] and several such letters, with the seals still unbroken, have been found by the excavator. The aim of the signet in this connection was of course to afford proof of the identity of the sender, and to warrant the contents of the letter. The importance attached to the seal at present in the East is so great, that without one no document is regarded as authentic. From the use for authenticating documents, the seal came to be employed for another purpose—that of authenticating the purity or weight of a piece of gold or other metal; the stamp upon the coin being the government guarantee of the fineness and weight of the piece of metal. It has often been supposed that the specimens of the scarab class of Egyptian seals were used as tokens of value, that they represented the small change of the Pharaohs. In support of this interpretation a remark of Plato, to the effect that “in Ethiopia engraved stones were used as money,” has often been quoted. It is of course true that the Egyptians had no coined money of their own before the time of the Macedonian Conquest; taxes were collected and salaries were paid in kind, and all trade was done by barter, as in Central Africa at the present day. The idea, however, that scarabs themselves were used for the purposes of barter, or as tokens of exchange, is not supported by the inscriptions, or by any of the scenes depicted on the monuments. But we do find, and this is very important, that during the Hyksos period (_circa_ 1700 B.C.),[19] and later under Amenhetep III (_circa_ 1400 B.C.),[20] the _Khetem_ or “seal” is given as a measure of value, although here it is probable that it was not the seal itself that is meant, but the _impression_ of it upon another substance. The Athenian General Timotheus, Polyaemus relates, being in want of money to pay his troops, “issued his own seal” for coin, and this substitute was accepted by the traders and market people confiding in his honour. This can only mean that _impressions_ of his signet on clay, or some other substance, were put into circulation as representatives of value, and so received by the sellers. It is in the impression of a seal or stamp upon a piece of gold or other metal that we have the origin of coined money.