The Roman aureus furnishes the type which is reproduced in the Sassanian gold coins, while the silver coins follow the standard long established in Western Asia, first under the Seleucid, and then under the Arsacid princes.

This standard is based upon the Attic drachm, which was adopted by Alexander as the basis of his monetary system.

The curious occurrence of a completely different standard for gold and silver in Persia during this period is accounted for by the circumstances of the time at which the coinage took its rise.

The Arsacidae had employed no gold coins, but had been content with a silver currency; any gold coin that may have been in use among their subjects for purposes of trade during the continuance of their empire must have been foreign money--Roman, Bactrian, or Indian; but the quantity had probably for the most part been very small.

But, about ten years before the accession of Artaxerxes there had been a sudden influx into Western Asia of Roman gold, in consequence of the terms of the treaty concluded between Artabanus and Macrinus (A.D.