Gregory XIII was a canon lawyer who had taught at Bologna and served at the Council of Trent, and he read the council's decrees as an instruction to rebuild the clergy through education. His answer was institutional. He endowed the Roman College of the Society of Jesus on a scale that let it become the model Catholic university of the age, and it carries his name still as the Pontifical Gregorian University. Around it he founded or funded a ring of national colleges in Rome, among them the English, German and Hungarian, Greek, Maronite and Armenian foundations, each training priests to be sent back into territory the church had lost or never held. The English College in particular supplied the missionary priests who entered Elizabethan England at the risk of execution.
Against that record stands the reaction to the news from Paris. On and after 24 August 1572, weeks into his pontificate, thousands of French Protestants were killed in the Saint Bartholomew's Day massacre, beginning in Paris and spreading to provincial towns. Rome received the killings as a deliverance of the church from a Huguenot conspiracy. Gregory XIII had a Te Deum sung, ordered a jubilee of thanksgiving, struck a commemorative medal, and commissioned Giorgio Vasari to paint the events in the Vatican.
Historians differ over how much he understood of the scale and character of the killings when he responded, and the medal and frescoes are sometimes read as a reaction to a reported political victory rather than to a massacre of civilians. What is not in dispute is that the celebration happened and that it was public, and it is the fact most often set beside the calendar when his reign is weighed.