The twelfth century ranks along with the fifth and the sixteenth as one of the more momentous periods in the life of the Church in Ireland when the course of its development was fundamentally changed. It was altered in a double way. The first was as part of a natural process of healthy growth wherein Ireland shared in that common experience of Latin Christendom when for a century and perhaps more, from mid-eleventh to mid-twelfth century, vigorous reform called a new religious spirit to life. The aggiornamento of the twelfth century brought great change to Ireland too, and however one might choose to define the historian's label ‘Gregorian reform’, there can be no doubt that Ireland participated in it to a considerable degree. Some historians have spoken of this period as one of ‘ecclesiastical revolution’ in the life of the Irish Church and it is hard to say that this is an exaggerated judgment. For its fruits can be seen in the propagation of a radical programme of moral and social reform, in the diminution of internal feuds and racial conflicts to permit the achievement of ecclesiastical unity, in a new diocesan structure which ousted the vested interests of centuries of steady family accumulation of ecclesiastical wealth and influence, in a zealously reforming episcopate. Harmonious relationships were established outside Ireland. There were introduced the most developed types of monasticism which in turn stimulated a revival of the older traditionally Irish Columban type. The connexion with Rome was inestimably strengthened.