Roughly fifty years after the last saint of this study died (Samthann, in 739), raiders commonly called Vikings arrived from Scandinavia, with Darerca's Killevy perhaps among the first attacked. Their raids significantly impacted Ireland, but paled in comparison with the invasion centuries later by descendants of their descendants in France, the Normans, after their conquest of England. Vikings settled in Ireland as well, known as the Hiberno-Norse after making cities like Dublin, Waterford, and Limerick their own. Intermarriage and alliances occurred, as in the case of Gormlaith (d. 1030), the daughter of one Leinster king and sister of another. Gormlaith wed one king of Dublin and was mother of another, the long-ruling Sitric Silkenbeard, before she became the wife of arguably the greatest Munster king (Brian Boru) and mother of another, with Brian and Gormlaith marrying at the same time Brian's daughter Sláine wed Sitric. To some extent, however, the Hiberno-Norse remained in their urban pockets by the Irish shore.

Such was not the case in France, where over generations the heathen Norse Vikings became the Christian Normans of Normandy, so integrating into western Christendom's channels of power that popes blessed two of their invasions of longstanding Christian countries—England in 1066 and then, as Anglo-Normans, Ireland roughly a century later. Both invasions transformed Europe in the process, although only the former could properly be considered a “conquest,” the latter more accurately a colonization. In France, the Norse-cum-Normans became “more French than the French,” a trend that would also be noted of their descendants in Ireland centuries later. Ethnic divisions in Ireland between Gaelic Irish and Anglo-Norman, later Anglo-Irish, remained both sharp and blurred, depending on the context, but the “Hiberniores ipsis Hibernis,” English colonists in Ireland who became “more Irish than the Irish themselves,” compiled perhaps one, and possibly two, of the three great collections of Irish saints’ Lives, known as the vitae sanctorum Hiberniae, preserving invaluable links to Ireland’s earlier medieval Christian heritage.

The century in which the Anglo-Normans invaded Ireland was one of the most momentous in western European history. Cities took shape, universities emerged out of monastic schools, and trade increased, giving rise to what would become the middle class and greater disposable movable wealth.