The greatest bishop of the West in these times was St. Ambrose, of Milan. He was born about the year 340, and thus was ten or twelve years younger than St. Basil and St. Gregory of Nazianzum. His father had held a very high office under the emperors; Ambrose himself was brought up as a lawyer, and had risen to be governor of Liguria, a large country in the north of Italy, of which Milan was the chief city.

The bishop of Milan, who was an Arian, died in the year 374, and then a great dispute arose between the orthodox and the Arians as to choosing a new bishop, so that it seemed as if they might even come to blows about it. When both parties were assembled in the cathedral for the election, the governor, Ambrose, went and made them a speech, desiring them to manage their business peaceably, and it is said that, as soon as be had done, a little child's voice was heard crying out "Ambrose bishop!" All at once, the whole assembly caught up the words, which seemed to have something providential in them; and they insisted that the governor should be the new bishop. Now although Ambrose had been brought up as a Christian, he was still only a catechumen, and had never thought of being a bishop, or a clergyman of any kind; and he was afraid to undertake so high and holy an office. He therefore did all that he could to get himself excused. He tried to make the people of Milan think that his temper was too severe, but they saw through his attempts. He then escaped from the town more than once, but he was brought back. Valentinian, who was then emperor, approved the choice of a bishop; and Ambrose was first baptized, and a few days afterwards he was consecrated.

He now studied very hard, in order to make up for his want of preparation for his office. He was very active in all sorts of pious and charitable works, and he soon became famous as a preacher. His steady firmness in maintaining the orthodox faith was especially shown when Valentinian's widow, Justina, who was an Arian, wished to take one of the churches of Milan from the Catholics and to give it to her own sect; and after a hard struggle, Ambrose got the better of her. He afterwards gained a very great influence both over Justina's son, Valentinian II, and over his elder brother Gratian. And when Gratian had been murdered by the friends of Maximus (the same Maximus who put Priscillian to death), and Theodosius came into the West to avenge his murder (AD 388), Ambrose had no less power with Theodosius than he had had with the younger emperors.

Theodosius took up his abode for a time at Milan after he had defeated and slain the usurper Mandamus. Soon after his arrival in the city, he went to service at the cathedral, and was going to seat himself in the part of it nearest to the altar, as at Constantinople the emperor's seat was in that part of the church. But Ambrose stopped him, and told him that none but the clergy were allowed to sit there; and he begged the emperor to take a place at the head of the people outside the altar-rails. Theodosius was so far from being angry at this, that he thanked the bishop, and explained to him how it was that he had made the mistake of going within the rails, and when he got back to Constantinople, he astonished his courtiers by ordering that his seat should be removed to a place answering to that in which he had sat at Milan, for that, he said, was much more seemly and proper.

There are other stories about Ambrose's dealings with Theodosius, but I shall mention only one, which is the most famous of all. One day when there was to be a great chariot race at Thessalonica, it happened that a famous charioteer, who was a favourite with the people of the town, had been put in prison by the governor on account of a very serious crime. On this a mob went to the governor, and demanded that the man should be set at liberty. The governor refused; and thereupon the mob grew furious, and murdered him, with a number of his soldiers and other persons. The emperor might have been excused for showing hearty displeasure at this outrage; but unhappily the great fault of his character was a readiness to give way to violent fits of passion; and on hearing what had been done, his anger knew no bounds. Ambrose, who was afraid lest some serious mischief should follow, did all that he could to soothe the emperor, and got a promise from him that the Thessalonians should be spared. But some other advisers afterwards got about Theodosius, and again inflamed his mind against the offenders, so that he gave orders for a fearful act of cruel and treacherous vengeance. The people of Thessalonica were invited in the emperor's name to some games in the circus or amphitheatre, which was a building open to the sky, and large enough to hold many thousands. And when they were all gathered together in the place, instead of the amusement which had been promised them, they were fallen on by soldiers, who for three hours carried on a savage butchery, sparing neither old men, women, nor children, and making no difference between innocent and guilty, Thessalonian or stranger. Among those who had come to see the games there was a foreign merchant, who had had no concern in the outrage of the mob, which was punished in this frightful way. He had two sons with him, and he offered his own life, with all that he had, if the soldiers would but spare one of them. The soldiers were willing to agree to this, but the poor father could not make up his mind which of the sons he should choose; and the soldiers, who were too much enraged by their horrid work to make any allowance for his feelings, stabbed both the youths before his eyes at the same moment. The number of persons slain in the massacre is not certain; there were at least as many as seven thousand, and some writers say that there were fifteen thousand.

When Ambrose heard of this shocking affair, he was filled with grief and horror, for he had relied on the emperor's promise to spare the Thessalonians, and great care had been taken that he should not know anything of the orders which had been afterwards sent off. He wrote a letter to Theodosius, exhorting him to repent, and telling him that, unless he did so, he could not be admitted to the Holy Communion. This letter brought the emperor to feel that he had done very wrongly; but Ambrose wished to make him feel it far more. As Theodosius was about to enter the cathedral, the bishop met him in the porch, and, laying hold on his robe, desired him to withdraw, because he was a man stained with innocent blood. The emperor said that he was deeply grieved for his offence; but Ambrose told him that this was not enough -- that he must show some more public proofs of his repentance for so great a sin. The emperor withdrew accordingly to his palace, where he shut himself up for eight months, refusing to wear his imperial robes, and spending his time in sadness and penitence. At length, when Christmas was drawing near, he went to the bishop, and humbly begged that he might be admitted into the Church again. Ambrose desired him to give some substantial token of his sorrow, and the emperor agreed to make a law by which no sentence of death should be executed until thirty days after it had been passed. This law was meant to prevent any more such sad effects of sudden passion in princes as the massacre of Thessalonica. The emperor was then allowed to enter the church, where he fell down on the pavement, with every appearance of the deepest grief and humiliation; and it is said that from that time he never spent a day without remembering the crime into which his passion had betrayed him.

Theodosius was the last emperor who kept up the ancient glory of Rome. He is called "the Great", and in many respects was well deserving of the name. He died in 395, and St. Ambrose died within two years after, on Easter eve, in the year 397.