This Romanesque and Norman cathedral has had a rough time of it since Roger II ordered it built in 1160. Henry VI, the Holy Roman Emperor, attended its consecration in 1197. The 1908 quake and a 1943 Allied firebombing didn't help. The cathedral has more or less been reconstructed from scratch, although some original architectural features remain.

Its central doorway was reconstructed using fragments originally from the 15th century. The lower part of the facade is decorated with 15th-century carvings depicting Sicilian agrarian life. The gray-and-pink interior has a trio of aisles divided by ogival arches and columns, resting under a trussed and painted ceiling. Many of the duomo's treasures were re-created, using fragments pulled from the ruins after the Allied bombings.

The statue of John the Baptist in the south aisle is attributed to Antonello Gagini in 1525. Dominating the main altar is a copy of the Byzantine Madonna della Lettera, the original having been destroyed by the 1943 firebombing. A pupil of Michelangelo, Jacopo del Duca, designed the Cappella del Sacramento in the north apse. It holds the cathedral's only original mosaic, a 14th-century work that depicts the Virgin seated with saints, queens, and archangels.

The church's treasure-trove is found in its Tesoro, which contains valuable candlesticks, chalices, and gold reliquaries. Much of the silverwork was created by artisans from Messina in the 17th and 18th centuries. Displayed for the first time in 3 centuries is the Manta d'Oro (golden mantle), a special cover for the Virgin and Bambino on the Duomo's altar.