St. Peter and St. Paul.
Twelfth-century mosaics in the Cathedral of Monreale, Sicily. (Illustration Credit i1.1)

The Crypt of the Popes, Catacomb of San Callisto, Rome, third century. Now empty, it once contained the remains of nine popes and eight bishops of the third century. (Illustration Credit i1.2)

The Mausoleum of Theodoric, Ravenna. Raising that single monolith that forms the roof was an astonishing achievement for the sixth century. The mausoleum also contains the sarcophagus of Pope Victor II (1055–1057). (Illustration Credit i1.3)

Justinian and his entourage, including Archbishop Maximian. The shield carrier on the far left is thought to be Belisarius.
Contemporary mosaic, sixth century, San Vitale, Ravenna. (Illustration Credit i1.4)

The Empress Theodora and her court.
Contemporary mosaic, sixth century, Church of San Vitale, Ravenna. (Illustration Credit i1.5)

St. Gregory the Great (590–604) in his study. The Holy Ghost whispers in his ear. Below, scribes are busy copying his work. Tenth-century ivory, Kunsthistorisches Museum, Vienna. (Illustration Credit i1.6)

Constantine the Great (708–715) presents Pope Sylvester with the tiara. Behind him is the pope’s horse; when Sylvester mounts it, the emperor will hold his stirrup as the traditional mark of respect. Thirteenth-century fresco, Church of the Santi Quattro Coronati, Rome. (Illustration Credit i1.7)

Pope Joan (?855–857) gives birth. Engraving, F. Spanheim, Histoire de la Papesse Jeanne, The Hague, 1721. (Illustration Credit i1.8)

The coronation of Charles the Bald by Pope John VIII (872–882) in 875. Musée Condé, Chantilly. (Illustration Credit i1.9)

The Emperor Otto III, enthroned between representatives of the Church and laity. The Munich Gospels, Staatsbibliothek, Munich. (Illustration Credit i1.10)

Equestrian statue of the Emperor Marcus Aurelius. It stood outside the Lateran Palace in the Middle Ages, when it was believed to represent Constantine the Great. Piazza del Campidoglio, Rome. (Illustration Credit i1.11)

The greatest pope of the Middle Ages, Innocent III (1198–1216). Thirteenth-century fresco, Monastery of Sacro Speco, Subiaco. (Illustration Credit i1.12)

Pope Boniface VIII (1294–1303) inaugurates, from the benediction balcony of the Lateran Palace, the first Jubilee in 1300. Biblioteca Ambrosiana, Milan. (Illustration Credit i1.13)

Christ presents the keys to St. Peter. Fresco by Pietro Perugino, Sistine Chapel, Rome. (Illustration Credit i1.14)

Pope Alexander VI (1492–1503) at prayer. Detail from Resurrection fresco by Pinturicchio, Borgia Apartments, Vatican Palace, Rome. (Illustration Credit i1.15)

Pope Julius II (1503–1513) toward the end of his life. Raphael, National Gallery, London. (Illustration Credit i1.16)

Pope Pius II (1458–1464) at Ancona, awaiting the arrival of the princes of Europe for a Crusade. Pinturicchio, Piccolomini Library, Siena Cathedral. (Illustration Credit i1.17)

Pope Leo X (de’ Medici, 1513–1521) and his nephews. Painted by Raphael in 1518, soon after Leo had appointed him architect of the new St. Peter’s. Galleria degli Uffizi, Florence. (Illustration Credit i1.18)

Pope Clement VII (de’ Medici, 1523–1534). It was he who refused to allow the annulment of Henry VIII’s first marriage and endured the sack of Rome in 1527. Sebastiano del Piombo, Museo di Capodimonte, Naples. (Illustration Credit i1.19)

Pope Paul III (Farnese, 1534–1549). Father of four illegitimate children before his election. One of two portraits by Titian, Museo di Capodimonte, Naples. (Illustration Credit i1.20)

Pope Paul V (Borghese, 1605–1621). An arch-reactionary, he first took issue with Galileo for his espousal of Copernicus’s theory that the sun, rather than the earth, was the center of the universe. Gianlorenzo Bernini, Statens Museum for Kunst, Copenhagen. (Illustration Credit i1.21)

Pope Innocent X (Pamfili, 1644–1655). Dominated through most of his reign by his reputed mistress, the sinister and corrupt Olimpia Maidalchini. Velazquez, Galleria Doria Pamphilj, Rome. (Illustration Credit i1.22)

Pope Pius VII (Chiaramonti, 1800–1823). Obliged to deal as best he could with Napoleon, who treated him abominably. Jacques-Louis David, Musée du Louvre, Paris. (Illustration Credit i1.23)

December 2, 1804: The Emperor Napoleon crowns himself and the Empress Josephine in Notre Dame, watched by Pope Pius VII on right, seated. Jacques-Louis David, Musée du Louvre, Paris. (Illustration Credit i1.24)

Pope Pius IX (1846–1878) and King Victor Emmanuel II. Popular print. (Illustration Credit i1.25)

Pope Leo XIII (1878–1903). Mass-produced popular print, Museo del Risorgimento, Milan. (Illustration Credit i1.26)

Pope Pius XII (1939–1958) at his coronation in 1939, seated on the sedia gestatoria. (Illustration Credit i1.27)

Pope John Paul I (1978): his first blessing from the balcony overlooking St. Peter’s Square. (Illustration Credit i1.28)

Pope John Paul II (1978–2005), obliged to use his Popemobile after an attempt on his life in 1981. (Illustration Credit i1.29)