Carlo, a Roman saint, was the son of Ghilberto Borromeo, Count of Arona, and of Mary of Medici, and was born at the castle of Arona, upon the Lago Maggiore, in the Milanese, Oct. 2, 1538. When he was about twelve years old, Julius Caesar Borromeo resigned to him an abbacy, the revenue of which he applied wholly in charity to the poor. He studied the civil and canon law at Pavia under the learned Francis Alciat. In 1554 his father died; and, although he had an elder brother, Count Frederick, he was requested by the family to take the management of their domestic affairs. After a time, however, he resumed his studies, and in 1559 he took his doctor's degree. In the following year his uncle Cardinal de' Medici was raised to the pontificate, by the name of Pius IV.; and Borromeo was made protonotary, intrusted with both the public and privy seal of the ecclesiastical state, created cardinal deacon, and soon after archbishop of Milan. In compliance with the pope's desire, he lived in great splendour; yet his own temperance and humility were never brought into question. He established an academy of select and learned persons, each of whom was to write on some chosen subject, either in verse or in prose, and to communicate to the society the fruits of his studies. The works thus produced were published in several volumes at Venice in 1748, under the title of Noctes Vaticanae. About this time he also founded and endowed a college at Pavia, which he dedicated to Justina, virgin and martyr.

Upon the death of his elder brother Frederick, his friends, and even the pope himself, advised him to quit the church, and marry, that his family might not become extinct. Contrary to expectation, however, he declined the proposal; and from that time became more fervent than ever in the exercises of piety, and more zealous for the advancement of ecclesiastical knowledge.

On the death of Pius IV., January 7, 1566, the skill and diligence of Borromeo materially contributed to stifle the cabals of the conclave. As soon as tranquillity had been re-established, Borromeo devoted himself wholly to the reformation of his large and important diocese, where the most flagitious irregularities were openly practised. He began by making pastoral visits in his metropolis; and by a variety of wise and necessary regulations, he soon restored proper decency and dignity to divine service. In conformity to the decrees of the council of Trent, he cleared the cathedral of its gorgeous tombs, rich ornaments, banners, arms, &c., sparing not the monuments even of his own relations. Nor did his zeal stop here. He divided the nave of the church throughout its whole length into two compartments, so that the sexes, being separated, might perform their devotions with feelings suitable to the place. He proceeded next to the collegiate churches, and even to the fraternities of penitents, particularly that of St John the Baptist. The reformation of the monasteries followed that of the churches; and the vigilance of the archbishop soon extended itself from the city to the country round it. The great abuses which had overrun the church at this time arose principally from the ignorance of the clergy. In order, therefore, to attack the evil at its root, Borromeo established seminaries, colleges, and communities, for the education of young persons intended for holy orders. He met with much opposition in his endeavours to bring about a reformation of manners; but by an inflexible constancy, tempered with great sweetness of manners, he prevailed against every obstacle, and succeeded in rendering the most important services to the cause of morals as well as religion. The governor of the province, and many of the senators, apprehensive that the cardinal's ordinances and proceedings would incroach upon the civil jurisdiction, addressed many remonstrances and complaints to the courts of Rome and Madrid. These, however, in as far as concerned the king of Spain, Philip II., were referred entirely to the decision of the pope. But Borromeo had more formidable difficulties to struggle with, in the inveterate opposition of several religious orders, particularly that of the Brothers of Humility. Three provosts of the society entered into a conspiracy to cut him off; and one of their confederates, Jerome Donat, surnamed Farina, took upon him to carry the design into execution. For this purpose he mixed with the crowd in the archiepiscopal chapel, where Borromeo spent an hour every evening in prayer with his domestics and other pious persons; and having watched his opportunity, he fired at him with a heavily loaded arquebus. The shot, strange to say, took no effect, though it was affirmed to have ruffled the rochet of the cardinal. His escape was believed to be miraculous, and was certainly wonderful, considering that the assassin had taken his station within five or six paces of his intended victim. At the moment when the shot was fired the choir were chanting the fine old melody, Non turbetur cor vestrum neque formidet; and it is said that the cardinal continued the service without any apparent emotion.

In the year 1576 the city and diocese of Milan were visited by the plague, which swept away great numbers. On this occasion Borromeo, with a spirit truly Christian and heroic, went about giving directions for accommodating the sick and burying the dead, avoiding no danger, and sparing no expense. Nor did he content himself with establishing proper regulations in the city, but went into all the neighbouring parishes where the contagion raged, distributing money, providing accommodation for the sick, and punishing those, especially the clergy, who were remiss in discharging the duties of their calling. Notwithstanding the fatigue and perplexity which he experienced in thus executing his pastoral charge, he abated nothing of the usual austerity of his life; bread and water constituting his humble daily fare.

But continual labours and austerities combined to shorten his valuable life. He was seized with an intermittent fever, and died at Milan, Nov. 4, 1584. He was immediately worshipped as a saint, but was not canonized till 1610. Besides the Novitates Vaticanæ, to which he appears to have contributed, the only literary relics of this intrepid and zealous reformer are some homilies, discourses, and sermons, with a collection of letters. Several lives of him have been published, viz., by Goleau; by Touron, a Dominican; by Ribadencia, a Spanish Jesuit; and by Bimeus, and others. Through all the mist of absurdity and superstition in which the character and actions of Borromeo have been involved, it may safely be affirmed that if the Church of Rome had had many such men, religion might have been spared some grievous wounds, and Europe many afflicting and sanguinary convulsions.

Frederigo, nephew or cousin-german of the preceding, and likewise a cardinal and bishop of Milan, is chiefly known as the founder of the Ambrosian library. See Libraries. He died A.D. 1632. He was the author of Meditamenta Litteraria (published in 1633, 4to), and some other works.