In 374 the bishopric of Milan fell vacant and when Ambrose tried to pacify the conflict between the Catholics and Arians over the appointment of a new bishop, the people turned on him and demanded that he become the bishop himself. He was a layman and not yet baptized (at this time it was common for baptism to be delayed and for people to remain for years as catechumens), but that was no defence. Coerced by the people and by the emperor, he was baptized, ordained, and installed as bishop within a week, on 7 December 374.

  He immediately gave his money to the poor and his land to the Church and set about learning theology. He had the advantage of knowing Greek, which few people did at that time, and so he was able to read the Eastern theologians and philosophers as well as those of the West.

  He was assiduous in carrying out his office, acting with charity to all: a true shepherd and teacher of the faithful. He was unimpressed by status and when the Emperor Theodosius ordered the massacre of 7,000 people in Thessalonica, Ambrose forced him to do public penance. He defended the rights of the Church and attacked the Arian heresy with learning, firmness and gentleness. He also wrote a number of hymns which are still in use today.

  Ambrose was a key figure in the conversion of St Augustine to Catholicism, impressing Augustine (hitherto unimpressed by the Catholics he had met) by his intelligence and scholarship. He died on Holy Saturday, 4 April 397.