The Duomo di Monreale (Monreale Cathedral) was originally established as a Benedictine monastery, situated on a hill overlooking Palermo. A papal bull in 1174 refers to the monastery being under construction, and in 1176 the first monks and abbot came to the monastery at the invitation of King William II of Sicily. The name "Monreale" was used for the first time in 1183 by Pope Lucius III.
At the west end of the cathedral, two square towers flank a portico built in 1770. The east end is covered in polychrome decoration of inlaid stone, in a pattern of intersecting arcades and roundels. The cathedral has a Latin cross plan, 102 m. long and 40 m. wide, with three naves separated by two rows on nine columns each. These columns, supporting pointed arcades, and their capitals are taken from Roman buildings and are all of granite, except for the first one on the right made of marble. The great apse of the nave is covered by a ribbed vault, with the other two apses topped by a half done, and the crossing has massive piers surmounted by a lantern with large windows. Polychrome wooden ceilings cover the rest of the church.
Today the cathedral is chiefly known for its interior mosaic decoration, and is considered the climax of Norman artistic production in Sicily.