An interesting passage in the _Book of Ely_ gives an idea of the activity of the Irish merchants at this period: “Certain merchants from Ireland, with merchandise of different kinds and some coarse woollen blankets, arrived at the little town called Grantebrycge (Cambridge) and exposed their wares there.”[138] It is not surprising then that the wealth of Ireland increased rapidly, so much so that Brian Borumha, realising that this was largely due to Viking enterprise, allowed the invaders to remain in their forts on the coast “for the purpose of attracting commerce from other countries to Ireland.”[139] And even after their defeat at Clontarf, the Vikings remained in the coast towns, whence they continued to engage in trade with England and the Continent. Both Giraldus Cambrensis[140] and William of Malmesbury[141] mention the extensive slave-trade carried on between Ireland and England in the twelfth century, Bristol being the chief centre. In addition to the slave traffic, large supplies of wine were imported from France, while the Irish ‘out of gratitude’ (_non ingrata_) gave hides and skins in exchange.[142] That there was commercial intercourse with Chester and also with the towns round the Bristol Channel may be seen from the names of the citizens of Dublin in the year 1200: Thorkaill, Swein Ivor from Cardiff; Turstinus and Ulf from Bristol; Godafridus and Ricardus from Swansea; Thurgot from Haverfordwest and Harold from Monmouth.[143] About 1170 two ships sailing from England “laden with English cloths and a great store of goods” were attacked and plundered near Dublin by a Norseman, Swein, son of Asleif; and some years later vessels from Britain carrying corn and wine were seized in Wexford harbour by the English invaders.[144]
The historical evidence is amply borne out by the existence of such old Norse loan-words in Irish as _mangaire_ (O.N. mangari, a ‘trader’), _marg_ (O.N. mörk, a ‘mark’), margadh, (O.N. markathr, a ‘market’), and _penning_ (O.N. penningr, a ‘penny’), and also by certain archæological discoveries. In Scandinavia coins of King Sithric Silken-Beard have been found,[145] while four sets of bronze scales and some weights richly decorated in enamel and gold have been dug up in Ireland (Bangor, Co. Down).[146] To the same period (early ninth century) also belong the scales and weights which were discovered in the great hoard at Islandbridge, near Kilmainham in 1866.[147] With such strong evidence of the influence exerted by the Vikings on the expansion of Irish trade it is not surprising to find that even as late as the seventeenth century the greater part of the merchants of Dublin traced their descent to Olaf Cuaran and the Dublin Norsemen.[148]