It is evident from the research of recent years that the lands constituting the Achaemenid Empire had inherited from earlier centuries two entirely separate currency systems. These systems continued in existence side by side until the last decades of the Empire. On the one hand, the territories south and east of the Taurus operated what can be described as a silver standard. The system, originated no doubt even as early as Sumer, and inherited by the Babylonians, had spread under the Assyrians, and later under the Achaemenids, to embrace Egypt, Syria, Eastern Anatolia, the Iranian Plateau and the Indo-Iranian borderlands. In those regions (though commodities such as gold, lead, corn, meat or wine may have served from time to time as media of payment), the most usual, and ultimate standard of worth was provided by fine silver. As necessary, this was tested for purity in the crucible, then reckoned for weight upon the scales, according to metrological standards already well established. Fundamentally, under this system, currency was silver – irrespective of the shape or form in which it was presented, and of whether or not it was made up in convenient units. There was no requirement for the silver to be offered in the form of coin, though during the 5th century B.C. and later it was often obtainable in that form. In particular, much silver coin arrived by trade and tribute from the states of the Aegean and the Greek world. Naturally such sources contributed an infinite variety of differing denominations and weight-standards, which, when lumped together, could not readily be reckoned by counting, but only on the balance, like the earlier bullion. Indeed, apart from the trading cities of Phoenicia and Southern Anatolia, there is no evidence that in Achaemenid times mint for coinage existed within the greater part of this silver-zone. The system did not require that pieces used in current transactions were necessarily adjusted to regular individual weights. There was no need for the stamp of an authority responsible for accuracy of weight or fineness. The only matters of consequence were total bulk weights, and the appearance of pure metal.