The Irish monks as the saviors of ancient libraries.

After the fall of the Roman Empire, any form of sophisticated culture that previously existed disasppeared in Western Europe. The Roman Empire of the East survived to the fall of Rome, but it was far too remote to make a difference. The barbarians took over, destroyed, pillaged and ransacked. The libraries, the repositories of all the ancient knowledge, disappeared:

The western empire was scarcely a memory now. The last Latin emperor had fallen just a few years after Patrick died. And though there was still a Greek emperor in the east at Constantinople, where a small, defensible state was long established on the Bosporus, he might as well have been at Timbuktu for all his law was known in western lands. All the great continental libraries had vanished; even memory of them had been erased from the minds of those who lived in the emerging feudal societies of medieval Europe.

(Cahill: p. 181)

To Cahill, it was the Irish monks who saved that very same ancient civilization that had otherwise disappeared:

Ireland, at peace and furiosuly copying, thus stood in the position of becoming Europe's publisher. But the pagan Saxon settlements of southern England had cut Ireland off from easy commerce with the continent. While Rome and its ancient empire faded from memory and a new, iliterate Europe rose on its ruins, a vibrant, literary culture was blooming in secret along its Celtic fringe. It needed only one step more to close the circle, which would reconnect Europe to its own past by way of scribal Ireland. (...) Columcille provided that step.

(Cahill: p. 183)

I'd say he is partially right. Yes, the Irish monks did salvage plenty of ancient books and, together with them, a good part of the old knowledge. However, we shouldn't forget the important role that Bizantium and, later on, the Arabs played in this story. It is to them that we owe the most important works from the Greek masters that survived throughout these difficult times. It would be a disservice to the historical truth to emphasize only the role of the Irish because they are "Western like us" and downplay the importance of the Greeks and, above all, the Arabs, who contributed their fair share to human knowledge during a few centuries before the Renaissance took off.

But there is one more fact that I consider of the utmost importance and that Cahill never seems to consider at all: human knowledge tends to flourish whenever there is a high density of population (which tends to be associated to urban settlements) and, above all, a high density of cultural exchanges (i.e., a rich flow of information). Neither of those things happened during the Middle Ages, a dark time when the rural lifestyle supplanted the cities and people lived in isolated communities. This wouldn't change until trade increased sometime in the 15th and 16th centuries and urban spots became important again. This is something to keep in mind at times like ours, when some people start hearing the beautiful chants of the rural life once again.