Pius IV (1499-1565), by backing the Council of Trent in its last and extremely tense period, emerged as one of the great popes of the Catholic Reformation. By his temperate and tractable approach, he broke with the severe regime of his predecessor, Paul IV.

Giovanni Angelo de' Medici, who became Pius IV, was born into the lesser nobility of Milan on March 31, 1499. His family was not related to the famous Medici of Florence. He received his early education at Pavia, and in 1525 he earned a doctorate in canon and civil law at the University of Bologna. The next year Medici began his service in the Church as a protonotary apostolic. Under Pope Paul III he gained a breadth of experience in administration within the papal states and in diplomacy on missions to Hungary and Transylvania. At the age of 46 Medici was ordained a priest. The same year, 1545, Paul III appointed him archbishop of Ragusa in Sicily and 4 years later raised him to the cardinalate. In 1556 Pope Paul IV assigned him to the archdiocese of Foligno. On Dec. 25, 1559, Medici was elected pope and took the name Pius IV.

Pius IV faced a serious challenge to his diplomatic finesse in the problem of the Council of Trent, which had been suspended since 1552. In 1562 the council was reassembled by his mandate. With astute diplomacy he guided the council's third period, the most stormy and difficult of all, to a successful conclusion on Dec. 4, 1563. During the remainder of his pontificate Pius IV implemented the Tridentine Decrees. In this task, as well as in the application of the Index and in supervising the work of the Inquisition, his sense of moderation and flexibility came to the fore. His sense of statesmanship and his smooth efficiency in administration also greatly aided him. One of Pius IV's chief aides was his nephew, Charles Borromeo, who served in the post of papal private secretary and whom Pius IV created a cardinal and archbishop of Milan in 1560.

Pius IV supported humanistic and artistic ventures in Rome in many ways. He encouraged Giovanni Pierluigi da Palestrina; he appointed to the cardinalate such eminent humanists as Girolamo Seripando, Stanislaus Hosius, and Guglielmo Sirleto; and he remained a loyal supporter of Michelangelo and heartened him in his work on the dome of the Basilica of St. Peter's. Various edifices and improvements in Rome bear his name: the Porta Pia on the Via Nomentana, the Borgo Pio, and the Villa Pia. Pius IV died in Rome on Dec. 9, 1565.

Further Reading

• Even though research calls for some modifications, the best modern comprehensive study of Pius IV is in Ludwig Pastor, History of the Popes, from the Close of the Middle Ages, vols. 15 and 16, translated by Ralph F. Kerr (1928), which contains a full bibliography and list of sources. For background consult Alexander Clarence Flick, The Decline of the Medieval Church, vol. 2 (1930), and Karl H. Dannenfeldt, The Church of the Renaissance and Reformation (1970).