Foreign commerce as well as domestic trade were greatly stimulated by the introduction of coinage and by the development of a ruder form of currency. Towards the end of the fourth century before the Christian era the Greeks of Massilia had introduced into Gaul gold coins of Philip of Macedon, which bore on the obverse a representation of the head of Apollo wreathed in laurel, and on the reverse a charioteer driving a pair of horses with the name _Philippos_ stamped underneath. On these coins the Gallic coinage was modelled, and the British coinage was derived mainly from that of Gaul or through Gaul from a Macedonian stater; for certain peculiarities are noticeable on our earliest coins which distinguish them from those of Gaul.[1020] Evidently a considerable time must have elapsed before the new art travelled from Southern to Northern Gaul, and again before it crossed the Channel; and it is only natural to find that the oldest and heaviest British coins weigh no more than a hundred and twenty grains, or thirteen grains lighter than the Philippus, although, on the other hand, they are heavier than Gallic coins which belong to the latter half of the second century before Christ.[1021] Until about a quarter of a century after Caesar’s invasion the British coins were uninscribed: indeed uninscribed coins were still current during the earlier years of the Roman occupation.[1022] Their weight gradually diminished; and gradually, owing to successive copying, the head of Apollo and his wreath, the charioteer, the chariot, and the horses became more and more conventionalized and degraded, the head in certain cases passing ultimately into a cruciform pattern or even into a four-leaved flower, the charioteer being evolved into pellets, and the pair of horses becoming first one, then more and more grotesque until it lost all resemblance to a quadruped. Die-sinkers (who were doubtless few) would use the same dies or follow the same general type during their working career; and new types appeared when their successors came to engrave new dies. By estimating the time which would have been required for these successive alterations, it has been calculated that the earliest British coins must have been struck about a hundred and fifty or perhaps two hundred years before the birth of Christ.[1023]