Denis Pétau (21 August 158311 December 1652), also known as Dionysius Petavius, was a French Jesuit theologian. Life Pétau was born at Orléans, where he had his initial education; he then attended the University of Paris, where he successfully defended his theses for the degree of Master of Arts, not in Latin, but in Greek. After this he followed the theological lectures at the Sorbonne, and, on the advice of Nicolas Ysambert, successfully applied for the chair of philosophy at Bourges. At Paris he formed a friendship with Isaac Casaubon, then librarian at the royal library, where he spent all his spare time studying the ancient Greek manuscripts. At Orléans he was ordained deacon and presented with a canonry. In 1603 he was appointed to a lectureship at the University of Bourges, but resigned his place two years later, in order to enter the Society of Jesus. After spending two years at Bourges he returned to Paris, and began a correspondence with Fronton du Duc, the editor of John Chrysostom. In 1605 he became a Jesuit, taught rhetoric at Reims (1609), La Flèche (1613), and at the Collège de Clermont (1618). During this last period he began a correspondence with the Bishop of Orléans, Gabriel de Laubépine (Albaspinaeus), on the first year of the primitive Church. Beginning in 1622, he taught positive theology for twenty-two years, and during this time he left France on only two occasions: first in 1629, to teach ecclesiastical history at Madrid at the invitation of Philip IV; second in 1639 to become a cardinal at Rome where Pope Urban VIII wanted him. At sixty years of age he stopped teaching, but retained his office of librarian, in which he had succeeded Fronton du Duc (1623), and devoted the rest of his life to his great work, the Dogmata theologica. He died in Paris. Works Continuing the chronological labours of Joseph Justus Scaliger, Pétau published in 1627 an Opus de doctrina temporum, which has been often reprinted. An abridgment of this work, Rationarium temporum, was translated into French and English, and has been brought down to the year 1849. The complete list of his works fills twenty-five columns in Sommervogel: he treats of chronology, history, philosophy, polemics, patristics, and the history of dogma. His first edition of the works of Synesius appeared in 1612, undertaken ten years earlier at the advice of Casaubon (Synesii episcopi Cyrenensis