In June 1170, Henry II was crowned the Young King at York. This was a breach of Canterbury’s privilege of coronation, and in November 1170 Becket excommunicated those who had crowned King Henry. Becket continued to excommunicate his opponents in the church, the news of which also reached Henry.
Upon hearing reports of Becket’s actions, Henry is said to have uttered words that were interpreted by his men as wishing Becket killed. The king’s exact words are in doubt and several versions have been reported. The most commonly quoted, as handed down by “oral tradition”, is “Will no one rid me of this turbulent priest?”
Whatever Henry said, it was interpreted as a royal command, and four knights, Reginald fitzUrse, Hugh de Morville, William de Tracy, and Richard le Breton, set out to confront the Archbishop of Canterbury.
On 29 December 1170 they arrived at Canterbury. According to accounts left by the monk Gervase of Canterbury and eyewitness Edward Grim, they placed their weapons under a tree outside the cathedral and hid their mail armour under cloaks before entering to challenge Becket. The knights informed Becket he was to go to Winchester to give an account of his actions, but Becket refused. It was not until Becket refused their demands to submit to the king’s will that they retrieved their weapons and rushed back inside for the killing. Becket, meanwhile, proceeded to the main hall for vespers. The four knights, wielding drawn swords, caught up with him in a spot near a door to the monastic cloister, the stairs into the crypt, and the stairs leading up into the quire of the cathedral, where the monks were chanting vespers.
Several contemporary accounts of what happened next exist; of particular note is that of Edward Grim, who was himself wounded in the attack. This is part of the account from Edward Grim:
…The wicked knight leapt suddenly upon him, cutting off the top of the crown which the unction of sacred chrism had dedicated to God. Next he received a second blow on the head, but still he stood firm and immovable. At the third blow he fell on his knees and elbows, offering himself a living sacrifice, and saying in a low voice, ‘For the name of Jesus and the protection of the Church, I am ready to embrace death.’ But the third knight inflicted a terrible wound as he lay prostrate. By this stroke, the crown of his head was separated from the head in such a way that the blood white with the brain, and the brain no less red from the blood, dyed the floor of the cathedral. The same clerk who had entered with the knights placed his foot on the neck of the holy priest and precious martyr, and, horrible to relate, scattered the brains and blood about the pavements, crying to the others, ‘Let us away, knights; this fellow will arise no more”
Read more about Thomas Becket and his relationship with King Henry II here: http://www.bbc.co.uk/history/british/middle_ages/becket_01.shtml