There was free intermarriage between Norse and Irish (_v. supra_, p. 56), but the strength of the clan-system kept the races distinct and there was no such infiltration of the whole population as took place in the English Danelagh. This system prevented any such settlement of Norsemen upon their own farms as took place in England, and the invaders lived almost entirely in the coast towns and the districts in their immediate neighbourhood, busying themselves with trade and shipping. Though the settlements were limited in their extent, we must not underrate their influence on Irish history generally. They gave the impetus there, as elsewhere, to the growth of town life, and from the period of Viking rule dates the origin of the chief Irish towns. To them also was due the great expansion, if not the birth, of Irish trade. Mention has been made of the wealth of Limerick (_v. supra_, p. 97), drawn chiefly from trade with France and Spain, and the other towns were not behind Limerick. The naval power of Dublin stretched from Waterford to Dundalk, the Irish channel swarmed with Viking fleets, and many of the shipping terms in use in Gaelic are loan-words from the Norse. It is probably to the trading activities of Vikings from the chiefs ports of Ireland that we owe the sprinkling of names of Norse origin which we find along the Welsh coast from the Dee to the Severn--Great Orm's Head, Anglesey, Ramsey I, Skokholm Island, Flat Holme and Steep Holme, and to them may be due the establishment of Swansea, earlier _Sweinesea_, Haverfordwest and possibly Bideford, as Norse colonies in the Bristol channel. We know in later times of several Norsemen who were living in Cardiff, Bristol, Swansea and Haverfordwest.