In the 700's, Ireland became subject to Scandinavian raids and emigrations, just as most of the rest of Europe. The first to arrive were the Norwegians who attacked various islands and some of the headlands; in the 800's, however, the Norwegians began to attack the western coast of Ireland. In the mid-800's and all through the 900's, the Norse actively began to build fortified towns along the eastern coast of Ireland. In 841, they built the fortified town of Dublin (which the Irish called Ath Cliath, or, "the hurdle ford"), and would later establish fortifications at Cork, Waterford, and Wicklow, some of the central towns of later Irish history. Of these towns, however, Dublin was the center of all the Norse activity and served as their central base for raids all around Ireland and the Irish Sea.
The Irish at this time did not concentrate their population along the coast but lived inland the Irish also did not live in large and fortified towns. The introduction of both fortifications and something resembling urban life was originally introduced by the Norse.
Eventually, however, the Norse would come in conflict with the Danish and the area around Dublin became part of the Danish kingdom that had been established in northern England. The Irish, however, lived in individual tribal groups that were not united it wasn't until 1014 that Munster Irish under the leadership of Brian Bóruma defeated the Danish at Clontarf and finally expelled the Norse for good.
The Norwegians and the Danish, however, had largely stripped Irish culture of its greatest cultural artifacts. The only histories that were written of the Norse in Ireland were written by the Irish these historians were far from sympathetic to the invaders! Ireland, however, gained a fundamental shift in its cultural and economic practices. The Irish inherited from the Danes and Norwegians fortified coastal towns and a new economy based on trade and commerce with other Europeans. They also gave to the Irish more sophisticated skills in ship-building and travel.
The most important legacy that the Irish bequeathed to Europe was Irish Christianity. When Patrick came to Ireland in the fifth century, Christianity had spread across the face of Celtic culture but hadn't really penetrated the various Celtic cultures. It was spread very thin and practiced by a perishingly small minority in Gaul and Britain. It was also assuming a new, distinct character among the Celts, who combined Christianity not only with native Celtic institutions and religions, but with a plethora of eastern mystery religions. (Much of what we call modern "paganism" which points to Celtic sources actually originates in eastern, mystery religions that had been imported into Celtic culture.) It was this Celticized version of Christianity that Patrick brought with him to Ireland.
The Saxon invasions, however, wiped out Christianity in England, but not in Wales or Ireland or Scotland, where the religion had been introduced by Columba, an Irish saint. It wasn't until the late sixth century that Christianity was reintroduced into Britain; this brand of Christianity, more aligned with the practices of the Roman church, came into conflict with Celtic Christianity and its unique practices. By the tenth century, the unique Celtic Christianity of Britain had largely been subordinated to Saxon Christianity.
It was in Ireland that Celtic Christianity thrived during the Germanic invasions and then the later subordination of Celtic Christian practices to Saxon practices.
The Christianity that Patrick brought to Ireland was
Christianity the standard form of Christianity in Roman occupied territories. Episcopal Christianity is oriented around the organization of Christians as lay people under the spiritual and partiall secular control of a bishop ("episcopus" in Latin). Episcopal Christianity, however, was wholly unsuited to Ireland, for it relies on a certain level of urbanization. For the largely rural, disorganized, and tribal nature of early Irish society, the episcopal structure had nothing to work with. So Irish Christianity soon developed into
Christianity, which is oriented around the centralization of a small Christian community under the leadership of an abbot. This would become the uniquely Irish form of Christianity that in spirit and in practice was much different from the predominantly episcopal character of Roman Christianity.
The monastic centers became the areas where Irish Christian culture thrived they also introduced some political stability and agriculture into Irish society. While they were nominally under the authority of Rome, because they were so removed they operated with relative independence. This would eventually bring them in severe conflict with the Roman church. Before that, however, Irish missionaries would spread Celtic culture and Christianity all over the face of Europe. Even though the Irish Christians eventually submitted to Roman pressures, Irish Christianity had diffused across the face of Europe.
This is because the most innovative and distinct feature of Irish Christianity was