As a result of the Synod of Kells in 1152, whereby Cardinal John Paparo came from Rome with the papal pallia for the newly formed Irish archdioceses, Canterbury lost its suffragan churches in Ireland, in particular Waterford and Dublin. It is said that Canterbury became vengeful and sent a mission to the Pope to protest. In 1155, king Henry II of England sent a delegation to Rome, as a result of which he received a papal letter known as Laudabiliter satis, which gave him the approval to conquer Ireland. It may be no coincidence that the pope in question, Adrian IV, was English and, therefore, may have been biased in favour of the king of England. However, if his motivation was purely political, it was certainly dressed-up to give the appearance of a religious crusade, whereby the English king would bring the primitive and antiquated Irish church back into the full authority of Rome. The reforms that St Malachy and others had worked so long and hard to achieve through peaceful negotiations were conveniently forgotten about by the new Pope, who now gave his blessing to English king to use the sword to modernise the Irish church.

Over the next few years, Henry II was consumed with wars in France, and simply didn’t have the time or resources to fulfill his plans for Ireland. Therefore, he may have recognised the opportunity that presented itself when Diarmaid Mac Murchadha approached him for help in 1166. No doubt he welcomed the news of Strongbow’s success in Ireland in 1170. However, the death of Diarmaid in May 1171 meant that Strongbow could now claim to have inherited his father-in-law’s Irish lands in Leinster. Henry II did not fully trust Strongbow’s loyalty. It must surely have crossed the king’s mind that Strongbow might declare himself king of his newly conquered lands in Ireland. Henry II now took the extraordinary decision to visit Ireland personally and establish his royal authority here.

Henry II landed near Waterford on 18th October, 1171 with a large contingent of knights and archers, as well as considerable quantities of food, wine, tools, and, not least, the royal tent. Among the first to meet the King of England was a deputation of citizens of Wexford, who brought with them Robert fitzStephen in chains. Robert had landed in Bannow in 1170 but was subsequently captured by the citizens of Wexford when the Norman force near the town had been depleted during the attack on Dublin led by Strongbow and Diarmaid Mac Murchadha. The Wexford men released Robert as a sign of their loyalty to the king. Strongbow also greeted the king, who granted him the lordship of Leinster as a chief tenant of the English crown, while retaining for himself the strategic ports of Dublin, Waterford and Wexford as part of the royal demesne.

While Henry was at Waterford, the first Irish king to submit to him was Diarmait Mac Cárthaig, who ruled Desmond (south Munster). From Waterford, Henry proceeded to Lismore, and then to Cashel. Near here, on the banks of the River Suir, he met Domnall Mór Ua Briain, king of Thomond (north Munster). From Cashel, Henry proceeded to Dublin, where he arrived on November 11th and was met by a variety of minor Irish kings, most notable among them being Tighearnán Ua Ruairc. Henry spent Christmas in Dublin, and left Ireland from Wexford on Easter Monday, 1172. 

When Henry II visited Cashel on his way from Waterford to Dublin, he decided that this was to be the location for an assembly of the ecclesiastical hierarchy of Ireland. He was now putting into action his papal mandate to bring about a complete reform of the Irish church. To differentiate it from the historic synod that was held here 70 years earlier, this would become known as the Council of Cashel and was held in the winter of 1171. Among those present were the archbishop of Cashel, Donnchad Ua hUallachain, the archbishop of Dublin, Lorcán Ua Tuathail, the archbishop of Tuam, Cadla Ua Dubhtaig, and the bishop of Lismore and papal legate, Gillacrist Ua Connairche who had attended the Synod of Kells in 1152. Henry II did not attend the Council himself, but was represented by several clerical officials while he monitored the proceedings from Dublin. The decrees that were agreed at the conclusion of the proceedings included that parishioners would pay tithes of animals or crops to their own church and that infants were to be baptised in consecrated fonts by priests. The effect was to bring the Irish church more in line with the observances of the English church.

During his stay in Ireland, Henry II’s royal army met no opposition. Instead, one by one the Irish kings came willingly to meet him. More significantly, they all agreed to recognise the English king as their overlord. There were, of course, some kings who were notable by their absence. One of those who had not submitted to Henry II while he was in Ireland was the most powerful of all the Irish kings, Ruaidrí Ua Conchobair. When he left, Henry sent emissaries to meet Ruaidrí somewhere on the River Shannon. The Irish king refused to submit, and continued for a number of years in the vain hope of banishing the new arrivals. However, Ruaidrí was unable to galvanise the local Irish kings into any alternative force that could counteract the Normans. Over the next few years, Ruaidrí frequently found himself in combat with rival Irish kings as much as the Normans themselves. By the end of 1174, Ruaidrí realised that his only option was a diplomatic solution. He sent emissaries to England who negotiated the Treaty of Windsor, which was signed on 6th October, 1175. One of the witnesses to this document was Lorcán Ua Tuathail, Archbishop of Dublin, who had also attended the Council of Cashel in 1171. As part of the Treaty of Windsor, Ruaidhrí had to swear fealty to Henry II, and renounce any claims to the lands conquered by the Normans (primarily Leinster, Meath and east Munster), while in turn the king of England recognised Ruaidhrí as lord of the rest of Ireland.