suzerainties to secure possession of his inherited realm. In 1162 he attempted to re-establish what he saw as his authority over the English Church by appointing his friend Thomas Becket as Archbishop of Canterbury upon the death of the incumbent archbishop, Theobald. Becket's defiance as Archbishop alienated the king and his counsellors. Henry and Becket had repeated disputes over issues such as church tenures, the marriage of Henry's brother, and taxation. Henry reacted by getting Becket and other English bishops to recognise sixteen ancient customs in writing for the first time in the Constitutions of Clarendon, governing relations between the king, his courts and the church. When Becket tried to leave the country without permission, Henry tried to ruin him by filing legal cases relating to Becket's previous tenure as chancellor. Becket fled and remained in exile for five years. Relations later improved, and Becket returned, but they declined again when Henry's son was crowned as coregent by the Archbishop of York, which Becket perceived as a challenge to his authority. Becket later excommunicated those who had offended him. When he received this news, Henry said: "What miserable drones and traitors have I nurtured and promoted in my household who let their lord be treated with such shameful contempt by a low-born clerk." Four of Henry's knights killed Becket in Canterbury Cathedral after Becket resisted a failed arrest attempt. Henry was widely considered complicit in Becket's death throughout Christian Europe. This made Henry a pariah; in penance, he walked barefoot into Canterbury Cathedral, where he was severely whipped by monks. From 1155 Henry claimed that Pope Adrian IV had given him authorisation to reform the Irish church by assuming control of Ireland, but Professor Anne Duggan's research indicates that the Laudabiliter is a falsification of an existing letter and that was not in fact Adrian's intention. It originally allowed Henry's brother William some territory. Henry did not personally act on this until 1171 by which time William was already dead. He invaded Ireland to assert his authority over knights who had accrued autonomous power after they recruited soldiers in England and Wales and colonised Ireland with his permission. Henry later gave Ireland to his youngest son, John. In 1172 Henry gave John the castles of Chinon, Loudun and Mirebeau as a wedding gift. This angered Henry's eighteen-year-old son, Henry the Young King, who believed these were his. A rebellion by