The Context and Development of Irish Literature:
History, Poetry, Landscape
 Part One: From Celtic to Christian, Pre-history to the twelfth century, page 2

True Irish history begins with the Celts, originally a northern European people who flourished throughout Europe from roughly the the 7th century B.C. up to about the first century B.C., when the expansion of the Roman Empire and the migrations of the Germanic and Slavic peoples constricted the Celts to the western islands.  The Celts likely entered Ireland, along with Wales and Scotland, perhaps as early as 500 B.C., and began what we now refer to as Irish civilization. The bulk of what I earlier called “traditional Irish mythology” emerges from the culture of these people and their relations with the Christian culture that followed them. Celtic culture was rich and diverse, with great skill in iron-making (their iron weapons made them formidable in battle), as well as agriculture, hunting, warfare, and road-building.  Their social structure was one of tribes and kings, governed by a system of laws and interpreted judgments called "Brehon Law,"and their religion was a kind of earth and sun worship known generally as "Druidism."  This culture was then radically transformed--though not entirely replaced--when in the early 5th century one of the Irish former British slaves, named Patrick, returned to Ireland and began the awesome project of converting the Celts to Christianity.

The result of Patrick’s mission was astonishing: in a rare peaceful conversion, Ireland was transformed into an almost entirely Christian community, covered with monasteries and abbies and dedicated to the task of preserving the classical learning that was rapidly being extinguished by the barbarians ravaging Europe during what we now term “the Dark Ages.”

View "Irish Monasteries"  

So successful were the Irish Priests in preserving this culture that they subsequently spread out to the rest of Europe and restored the classical learning, and many of the classical books, that otherwise would have vanished from the West.  For example, St. Columba sailed from Ireland to the island of Iona in 563 and established the great monastic community there.  As early as the 8th century, the Anglo-Saxon historian, "the Venerable Bede," wrote:  "At that time there were many of the English nation, both of noble and of lesser rank, who, whether for divine study or to lead a more continent life, had left their native land and had withdrawn to Ireland.  Certain among them gave themselves up willingly to the monastic way of life, while others rather went about from cell to cell of the teachers and took pleasure in cultivating study.  And all these the Irish most freely received, and made it their study to provide them with food from day to day without any charge, with books to read and with free teaching."  This has led to the idea that the Irish “saved western civilization,” a concept that has much truth, considered in a broad sense.