The example, once set, was quickly followed by the more important Greek cities, until by the middle of the sixth century the art of coinage had travelled from Ionia across the mainland of Greece to the colonies in Italy and Sicily. Owing to the peculiar political conditions of Greece, where every town held a separate and independent sovereignty, each state was jealous to assert its autonomy on its coins, with the result that the Greek coinage presents an enormous variety of types, held together, however, as the money of one people by the uniformity of their general character and of the art in which they are expressed. We may now proceed to consider a few representative coins, which in the midst of innumerable local issues were important enough by their purity of weight and metal, or by their abundance, or by the commercial reputation of their issuing states, to predominate in the Greek world as a sort of international currency and standard of exchange. The earliest electrum stater of Ionia is interesting on account of its fabric only, for it has no type. It is a bean-shaped lump of metal, one side of which has been stamped with a flat die marked with parallel scratches, the other with three punches, which have left deep impressions (No. =24=; fig. 12_a_). The pieces which immediately followed, such as the silver money of Aegina (No. =25=; fig. 12_d_), have a real type on the obverse, while the punch-mark on the reverse is more regular, and is often ornamented with some design of a special character, though it does not contain a type until later.