[84] Introduction to O'Curry's _Manners and Customs of the Ancient Irish_, Vol. I, pp. ccclxix _et seq._
According to Strabo the exports from Britain in the early part of the first century consisted of gold, silver, and iron, wheat, cattle, skins, slaves, and dogs; while the imports included ivory ornaments, such as bracelets, amber beads, and glass. Tin was exported from Cornwall to Gaul, and carried overland to Marseilles, but this does not appear to have been the earliest route. As has been indicated, tin appears to have been carried, before the Celts obtained control of British trade, by the sea route to the Carthaginian colonies in Spain.
The Carthaginians had long kept secret the sources of their supplies of tin from the group of islands known as the Cassiterides. About 322 B.C., however, the Greek merchants at Marseilles fitted out an expedition which was placed in charge of Pytheas, a mathematician, for the purpose of exploring the northern area. This scholar wrote an account of his voyage, but only fragments of it quoted by different ancient authors have come down to us. He appears to have coasted round Spain and Brittany, and to have sailed up the English Channel to Kent, to have reached as far north as Orkney and Shetland, and perhaps, as some think, Iceland, to have crossed the North Sea towards the mouth of the Baltic, and explored a part of the coast of Norway. He returned to Britain, which he appears to have partly explored before crossing over to Gaul. In an extract from his diary, quoted by Strabo, he tells that the Britons in certain districts not detailed grew corn, millet, and vegetables. Such of them as had corn and honey made a beverage from these materials. They brought the corn ears into great houses (barns) and threshed them there, for on account of the rain and lack of sunshine out-door threshing floors were of little use to them. Pytheas noted that in Britain the days were longer and the nights brighter than in the Mediterranean area. In the northern parts he visited the nights were so short that the interval between sunset and sunrise was scarcely perceptible. The farthest north headland of Britain was Cape Orcas.[85] Six days sail north of Britain lay Thule, which was situated near the frozen sea. There a day lasted six months and a night for the same space of time.