With this state of progress and prosperity the Danes played sad havoc.  Animated with the fiercest pagan fanaticism, they turned with fury against Christianity, and especially against monks and religious foundations.  Armagh, Clonmacnois, Bangor, Kildare, and many other great monastic establishments thus fell before their fury.  Ignorance, neglect of religion, and corruption of manners followed, and from the eighth to the twelfth century there was a noted falling off in the number of Irish scholars.  At home indeed were Cormac and Maelmurra, O’Hartigan and O’Flynn, and abroad was John Scotus Erigena, whose learning was so great that it excited astonishment even at Rome.  The love of learning and zeal for religion lived on through this long period of accumulated disasters.  After the triumph of Brian Boru at Clontarf, there was a distinct revival of piety and learning; and, when a century of turmoil followed Brian’s fall and religion again suffered, nothing was wanted to bring the people back to a sense of their duty but the energy and reforming zeal of St. Malachy.

Gerald Barry, the notorious Anglo-Norman, who visited Ireland towards the close of the twelfth century, has been convicted out of his own mouth when he states that Ireland was a barbarous nation when his people came there.  He forgot that a people who could illuminate the Book of Kells and build Cormac’s Chapel could not be called savages, nor could a church be lost to a sense of decency and dignity that numbered among its children such a man as St. Laurence O’Toole.  Abuses there were, it is true, consequent on long continued war, though these abuses were increased rather than lessened by the coming of the Anglo-Normans, and to such an extent that for more than two centuries there is not a single great name among Irish scholars except Duns Scotus.

The fame of Duns Scotus was European, and the Subtle Doctor, as he was called, became the great glory of the Franciscan, as his rival St. Thomas was the great glory of the Dominican, order.  But he left no successor, and from his death, at the opening of the fourteenth century, till the seventeenth century the number of Irish scholars or recognized Irish saints was small.  Yet, in the midst of disorders within, and despite oppression from without, at no time did the love of learning disappear in Ireland; nor was there ever in the Irish church either heresy or schism.

The attempted reformation by Henry VIII and his daughter Elizabeth produced martyrs like O’Hurley and O’Hely; and there were many more martyrs in the time of the Stuarts, and especially under the short but sanguinary rule of Cromwell.