In the eleventh and twelfth centuries the Church changed. A reformed papacy pushed a tight new order, ruled by powerful bishops, with the pope at their head as monarch.

The Irish Church looked back to seven centuries of Christianity and a golden age of literature and art. It had developed on its own with little attention from Rome. It had small local dioceses, supervised by bishops. But its powerful ancient monastic churches, towns rather than simple monasteries, were immensely rich, powerful and cultivated – Armagh, Clonmacnoise, Cork, Glendalough etc. Their great schools taught Latin, Irish, theology, philosophy, law, grammar, metrics, chronology, literature in Latin and Irish; their scriptoria produced exquisite illuminated manuscripts; their workshops did fine metal and stone work (churches, high crosses, round towers). Within them were different kinds of monasteries.

You may enter that island and do there what has to do with the honour of God and the salvation of the land.

Pope Adrian IV

The Irish responded to change. Reformers established large dioceses, with bishops, archbishops and a primate, in three great national synods – Cashel (1101), Ráith Bressail (1101), Kells (1152). They cut the long connection with Canterbury of Dublin, Waterford and Limerick. This embittered Canterbury. They would reform the morals of the laity, especially on marriage law. They would reform Irish monasteries by bringing in foreign orders.

Henry II of England lands in Waterford, October 1172. Illustration: James E Doyle/ Getty Images

The reorganisation of the dioceses – a managerial revolution – was successful. There was a down side. The new bishops had little property. To fund themselves, they asset-stripped the ancient monastic churches. The schools and workshops declined. Scholarship, art and high culture were impoverished. The bishops founded no cathedral schools and, later, no universities – a cultural disaster for Ireland.

The reformers’ plan for the sexual morals of the laity was loud-mouthed and uncritical. It focused mostly on the kings and aristocracy. These behaved as their peers in the rest of Europe, but the Irish reformers publicised everywhere their so-called “enormous vices”. Anselm of Canterbury was told that in Ireland “men exchange their wives for the wives of others as freely and publicly as a man might exchange his horse for a horse”. The leader of the reformers, St Malachy of Armagh (1095-1148), convinced St Bernard that the people of the diocese of Connor were pagan in fact. Bernard in his biography of Malachy (1149) published the libel: the Irish were barbarians, Christians in name, pagans in fact. Bernard’s work was read all over Europe. The story soon reached the papacy.

Henry II, king of England, held council in 1155 – his brother William, the archbishops of Canterbury and York, the bishop of London and others – to discuss his plan to invade Ireland. Already, there were two English embassies to the pope: one from Henry II, one from archbishop Theobald of Canterbury. Pope Adrian IV issued the papal privilege, Laudabiliter, to the second. Here the pope wrote : “You may enter that island and do there what has to do with the honour of God and the salvation of the land. And may the people of that land receive you with honour and revere you as their lord ... dearest son in Christ, you want to subject its people to the laws and to root out from it the weeds of vice ... We therefore duly favour your pious and praiseworthy desire ... and are well pleased to agree to that, to extend the boundaries of the Church, restrain vice, correct morals, implant virtues, increase the Christian religion, you may enter that island ... take care to form that nation with good morals.”

Henry did not come until 1171/2, after his subjects, Strongbow and others, had conquered most of Leinster. He landed in Waterford with a great army. The Irish kings collapsed like a house of cards. Dermot MacCarthy, king of Desmond, hurried to do homage, took an oath (of feudal fealty or simple loyalty), gave hostages, and promised to hold his kingdom for Henry II, under royal tribute. So did Domhnall Mór O’Brien, king of Thomond. So, also, the kings of Meath and the north-east. Rory O’Connor, the high-king, stood aloof, impotently. Not a sword was drawn in defence of their lands.

Henry II, (1133-89), the first Plantagenet king of England, authorisies Dermot MacMorrough, banished king of Leinster, to levy forces from among the English to try to regain his crown. Photograph: Getty Images

Henry, though under interdict for the murder of his archbishop Becket, summoned a council of the Irish Church at Cashel. The bishops came meekly to a council run by Henry’s programme manager, Ralf of Llandaff. They passed two remarkable resolutions; first, that the Irish church should be as much under the power of the king as the English church; and second, they granted the kingdom of Ireland, in writing, to Henry and his heirs forever. Ralf of Llandaff delivered these resolutions to pope Alexander III.

You have wonderfully and gloriously triumphed over that people of Ireland, who, ignoring the fear of God, in unbridled fashion wander at random through the depths of vice

The pope wrote to the Irish kings ordering them obey Henry II, “that powerful and majestic king who is a devout son of the church”, who would bring peace. He wrote to the Irish bishops: “With what shocking abuses the Irish people are infected and how, lapsed from the fear of God and reverence for the Christian faith ... has been made known to Us. ... The illustrious king of England, moved by divine inspiration ... has subjected to his rule that barbarous and uncivilised people, ignorant of the divine law. ...We command ... that you will diligently ... help the king, a great man and a devout son of the church, to maintain and preserve that land and to wipe out the filth of such an abomination.”

He wrote to Henry II: “With much joy, we have been assured that, like a pious king and magnificent prince, you have wonderfully and gloriously triumphed over that people of Ireland, who, ignoring the fear of God, in unbridled fashion wander at random through the depths of vice and have renounced all reverence for the Christian faith and virtue. ... You have extended the power of Your Majesty over ... a race uncivilised and indisciplined.” He says he “omits for the present other monstrous abuses which the same race, neglecting the observance of the Christian faith, irreverently practises”; he condemns the sexual perversity of the Irish and ends with a few more random denunciations.

So ended the reform of the Irish Church; so began, with papal approval, English rule in Ireland.

Donnchadh Ó Corráin is emeritus professor of medieval history at University College Cork. He is author of The Irish Church, its Reform and the English Invasion (Four Courts Press, €35