Caesar Baronius (October 31,1538— June 30,1607), Italian cardinal and ecclesiastical historian, was born at Sora, and was educated at Veroli and Naples. At Rome he joined the Oratory in 1557 under St. Philip Neri and succeeded him as superior in 1593. Pope Clement VIII, whose confessor he was, made him cardinal in 1596 and librarian of the Vatican.

At subsequent conclaves he was twice nearly elected pope, but on each occasion was opposed by Spain on account of his work on the Monarchy of Sicily, in which he supported the papal claims against those of the Spanish government. Baronius is best known by his Annales Ecciesiastici, undertaken by the order of St. Philip as an answer to the Magdeburg Centuries. After nearly thirty years of lecturing at the Vallicella on the history of the Church and being trained by St Philip as a great man for a great work, he began to write, and produced twelve folios (1588—1607).

In the Annales he treats history in strict chronological order and keeps theology in the background. In spite of many errors, especially in Greek history, in which he had to depend upon secondhand information, the work of Baronius stands as an honest attempt to write history, marked with a sincere love of truth. Baronius makes use of the words of St Augustine: "I shall love with a special love the man who most rigidly and severely corrects my errors." He also undertook a new edition to the Roman martyrology (1586), which he purified of many inaccuracies.