The first pontiff to be elected outside of Rome due to political instability in the city, Urban II launched the First Crusade in 1095 with his fiery speech at the Council of Clermont, igniting centuries of religious warfare between Christianity and Islam. Urban II called upon Western Europe’s Christians to help Eastern Christians reclaim the Holy Land from the Seljuk Turks, who had barred Christians from Jerusalem.

“When an armed attack is made upon the enemy,” he reportedly proclaimed, “let this one cry be raised by all the soldiers of God: ‘It is the will of God! It is the will of God!’” Knights, infantry and ordinary citizens heeded his call and joined the armed pilgrimage that captured Jerusalem in 1099. News of the victory, however, didn’t reach Rome until after Urban II’s death. The following two centuries brought eight major crusades, resulting in millions of deaths.

Known as the “warrior pope,” Julius II led military campaigns to free the Papal States from local rule, and in 1506, he founded the Swiss Guards, the colorful military force that continues to serve as the pontiff’s bodyguards.

A patron of the arts during the High Renaissance, Julius II is responsible for two of the most notable Vatican landmarks. He asked Michelangelo to pause work on his marble tomb and instead paint the ceiling of the newly constructed Sistine Chapel, the sacred space where cardinals gather in papal conclaves to elect new popes. In 1506, Julius II laid the first marble stone for a new St. Peter’s Basilica, a grand replacement for the 1,200-year-old original, and tasked architect Donato Bramante with its design.

Born into the powerful Medici family, Leo X funded some of the Renaissance’s most famous artworks and enjoyed the finer things in life. To finance the construction of St. Peter’s Basilica, military campaigns and his own personal extravagances, Julius II’s successor continued the practice of selling offices and indulgences—payments for the forgiveness of sins.

The pay-for-penance scheme and excesses of the Church’s hierarchy, epitomized by Leo X, provoked German priest and theologian Martin Luther to post his "95 Theses" in 1517, sparking the Protestant Reformation.

“Why does not the pope, whose wealth today is greater than the wealth of the richest Crassus, build the basilica of St. Peter with his own money rather than with the money of poor believers?” Luther asked. Leo X condemned the "95 Theses" as heretical and excommunicated Luther from the Church in 1521.

The longest-reigning elected pope, Pius IX served more than 31 years. In 1854, the pontiff established the dogma of the Immaculate Conception, which codified the long-held belief that Mary, the mother of Jesus, was born without original sin. To address the Church’s place in a rapidly modernizing society, the pontiff in 1869 convened the First Vatican Council, which decreed papal infallibility in matters of faith and morals.

In the temporal realm, the unification of Italy and the capture of Rome in 1870 brought the demise of the Papal States. Pius IX refused to recognize the newly unified Italian government and declared himself a “prisoner of the Vatican.” For almost 60 years, popes engaged in political protest by refusing to leave the Vatican and submit to the authority of the Italian government.

On Easter Sunday in 1949, Pius XII addressed the French people in the first televised papal message, allowing the pontiff to more directly communicate to the world’s Catholics. “It has been told to the world that religion is in decline,” the pope said during the broadcast, “and with the aid of this new wonder, the world will see the grand triumphs of the Eucharist and of Mary.”

Nine years later, Pius XII proclaimed 12th-century Saint Clare of Assisi the patron saint of television. Elected to the papacy just months before the start of World War II, Pius XII presided during one of the most challenging periods in global history, marked by war and the rise of authoritarian regimes. Critics have faulted his silence during the Holocaust and his failure to forcefully condemn the Nazis.

More accessible and less aloof than his predecessor, Pius XII, “Good Pope John” was beloved by many Catholics. Although his pontificate lasted less than five years, John XXIII initiated a period of major renewal and reform. He denounced antisemitism and promoted ecumenism and dialogue with other faiths. Seeking to modernize the Church, he convened the Second Vatican Council (also known as Vatican II) in 1962. John XXIII presided over the first session of the first ecumenical council in 92 years, just two weeks after receiving a fatal stomach cancer diagnosis.

“At least I have launched this big ship,” he told a cardinal. “Another will have the task of taking it out to sea.” His successor, Paul VI, oversaw the conclusion of Vatican II, which enacted sweeping liturgical changes, such as the replacement of Latin with native languages in liturgies and increased roles for the laity.

A native of Poland, John Paul II was the first-ever Slavic pope and first non-Italian pontiff elected in 455 years. The jet-setting pope, who spoke eight languages, traveled to more than 120 countries and often connected with audiences by speaking in their native tongues. His unwavering opposition to communism and support of the Solidarity trade union in Poland contributed to communism’s downfall in Eastern Europe.

Engaging in interfaith outreach, John Paul II was the first pope to visit a synagogue, a Protestant church and a mosque, and he delivered a sweeping public apology for the Church’s past wrongs, including the Crusades, Inquisition and treatment of Jews. After surviving a 1981 assassination attempt, the pontiff practiced what he preached and personally forgave his assailant after meeting him in prison. After his death, two million people filled St. Peter’s Square for his funeral, one of the largest in history.