What to see
The exterior blends different eras. The main facade is flanked by two towers—the left one unfinished at the first order, the southern one missing its spire after an 1807 lightning strike. A 1770 Baroque portico with Tuscan columns precedes the main entrance, which features bronze doors cast by Bonanno Pisano in 1185-1186. Along the northern side runs a Renaissance portico designed between 1547 and 1569 by Giovanni Domenico and Fazio Gagini, presenting eleven round arches, Corinthian columns, and a bronze portal crafted by Barisano da Trani in 1179.
Inside, the Clunian-inspired layout features a wide nave separated by columns of grey oriental granite and a single pillar of cipolin marble, topped with classical Corinthian capitals. The walls are covered by an astonishing 6,500 square meters (70,000 sq ft) of Byzantine-style glass mosaics, executed by Venetian and local masters from the late 12th to the mid-13th century. The triple choir contains an opus alexandrinum marble and porphyry pavement showing clear Arab influences. A catastrophic fire on November 11, 1811, destroyed the original Fatimid-style wooden roof, the walnut choir fittings, and the organs, while shattering the royal tombs. Today, the restored interior houses the porphyry sarcophagi of William I and William II, the tombs of Margaret of Navarre and her sons, and an urn holding the viscera of King Louis IX of France, who died in 1270. Later additions include the Baroque chapels of San Castrense (1595) and the Crucifix (1690-1692).
The adjacent 2,200-square-meter Benedictine cloister, completed around 1200, is surrounded by pointed arches supported by 216 white marble twin columns. These shafts are alternately plain or decorated with glass tesserae in gold and bright colors, leading up to intricately carved capitals depicting biblical scenes and allegories, alongside a square pillared lavatorium for the monks.
Visiting
Exploring the cathedral and its grounds reveals the remnants of a once-massive monastic precinct. Originally protected by a perimeter wall with twelve towers, only ruins of the towers and parts of the monks' dormitory remain today. Inside the church, visitors can observe the massive six-manual Ruffatti organ, featuring 102 stops, installed in 1967 to replace earlier instruments lost to fire and time.
Our editors' tip
When walking down the nave, pay close attention to the columns supporting the pointed arches. Amidst the uniform grey oriental granite, you will find exactly one column carved from cipolin marble—a deliberate architectural anomaly resulting from the medieval practice of repurposing classical Roman materials in new monumental constructions.