19 March. This day marks the reign of two Popes, Ugolino da Segni or Gregory IX (19 Mar 1227 – 22 Aug 1241) Giovanni de Medici or Leo X (11 Dec 1475 – 01 Dec 1521). Gregory IX is remembered primarily for establishing the Dominican-supervised Papal Inquisition and for canonizing Francis of Assissi, Anthony of Padua and Dominic. Leo X’s, on the other hand, is tied to the rise of the Protestant Reformation which was partly a reaction against his decision “to sell church offices and indulgences in order to pay off debts incurred” for the putting up of St. Peter’s Basilica and other ventures.
Source: Richard McBrien, Lives of the Popes: The Pontiffs from St. Peter to John Paul II (San Francisco: HarperSanFrancisco, 1997), p. 212, 272.