Pope Gregory XIII introduced the Gregorian calendar in 1582, which is still the most widely used calendar in the world today.

Pope Clement V moved the papal court to Avignon in 1309, beginning the Avignon Papacy, which lasted until 1377.

Pope Clement VII excommunicated King Henry VIII in 1533 after Henry's marriage to Anne Boleyn and his break with the Catholic Church.

Pope Urban II called for the First Crusade at the Council of Clermont in 1095.

Pope Gregory VII, also known as Hildebrand, is known for his Gregorian Reforms, which aimed to strengthen papal authority and reform the church.

Pope Pius IX was the last pope to be crowned in the Lateran Basilica in 1846.

Pope Julius II commissioned the construction of the new St. Peter's Basilica in 1506.

Pope Martin V was elected at the Council of Constance in 1417, ending the Western Schism.

Pope Sixtus IV was a patron of the arts and sciences, and commissioned the construction of the Sistine Chapel.

Pope Leo X was the pope during the early years of the Protestant Reformation, and issued the papal bull Exsurge Domine in 1520, condemning Martin Luther's teachings.

Pope Clement VI took measures to address the Black Death, including establishing quarantine measures and providing financial assistance to affected areas.

Pope Urban VI was elected in 1378, but a rival pope, Clement VII, was elected in Avignon, leading to the Great Schism.

Pope Gregory IX established the Inquisition in 1231 to combat heresy.

Pope Clement VI was the pope during the early years of the Hundred Years' War.

Pope John XXIII is known for his efforts to promote peace and reconciliation, and for convening the Second Vatican Council.