Anagni Cathedral rises on the acropolis of a town long associated with papal government. Bishop Pietro da Salerno began the present church in 1072, on a site with earlier sacred buildings, and construction continued until about 1104. The cathedral was dedicated to Santa Maria Annunziata and developed a Romanesque basilican form with a powerful bell tower. Medieval alterations later introduced Gothic elements. Its location above the Sacco Valley made the complex both a religious center and a visible statement of episcopal authority in southern Lazio.

The cathedral’s crypt, dedicated to Saint Magnus, became its artistic treasure. Teams of painters covered its vaults and walls in the thirteenth century with biblical narratives, saints, apocalyptic scenes, medical imagery, and an ordered vision of the cosmos. The pavement above and other parts of the church display Cosmatesque marble work associated with Roman craftsmen. Relics and local devotion drew worshippers, while the chapter and bishop maintained the cathedral as Anagni became a favored residence of medieval popes born in or connected with the region.

Beside the cathedral, a group of fortified houses evolved into the Papal Palace. Construction phases are complex, but the buildings are linked especially with the Conti family and Pope Gregory IX, formerly Cardinal Ugolino of Anagni. Pope Innocent IV was elected at Anagni in 1243, and the palace hosted meetings during the papacy’s struggles with Emperor Frederick II. Residential halls, towers, passages, and chapels combined security with the ceremonial needs of a traveling papal court, making Anagni an alternative center of church diplomacy and administration.

The best-known episode occurred in September 1303. Agents of King Philip IV of France, working with members of the Colonna family, entered Anagni and seized Pope Boniface VIII, a member of the local Caetani family. Tradition later condensed the assault into the “Slap of Anagni,” although the details remain disputed. Townspeople freed the pope after several days, but he died soon afterward in Rome. The confrontation became a symbol of weakening medieval papal claims and permanently linked Boniface’s name with the palace.

Later centuries brought reuse, subdivision, restoration, and changing ownership. The cathedral remained an active place of worship, while the palace eventually came under the care of the Cistercian Sisters of Charity and developed as a museum. Visitors now move through rooms associated with the medieval papal court and descend into the painted crypt, sometimes called the “Sistine Chapel of the Middle Ages.” Together the buildings preserve architecture, art, ritual, and political memory, explaining why Anagni’s identity as the “City of the Popes” rests on more than one celebrated confrontation.