"You can find images of his murder in churches across Latin Christendom, from Germany and Spain, to Italy and Norway. Becket was, and remains, a truly European saint," says Lloyd de Beer of the British Museum.
Last year 7,548 people from Ireland completed the pilgrimage to Santiago de Compostela; and in 2018 the Irish comprised the seventh-largest foreign nationality making the journey.
Francis used the occasion to speak of a possible joint pastoral visit with the Archbishop of Canterbury to South Sudan.
Head of the Church in England and Wales, Cardinal Vincent Nichols, gives address at symposium on St Thomas a Becket at Lambeth Palace.