The abbey was founded by William the Lion (1143-1214) in 1178 on his return from captivity, in memory of his childhood friend, Thomas Beckett, who had been murdered in Canterbury Cathedral eight years previously. The building was completed in 1233. A historic event took place here: the Declaration of Arbroath was drawn up and signed in the abbey on 6 April 1320, eloquently asserting Scotland's independence. It was dispatched to Pope John XXII, in exile in Avignon.