The Cathedral of Monreale is one of the greatest extant examples of Norman architecture in the world. It was begun in 1174 by William II, and in 1182 the church, dedicated to the Assumption of the Virgin Mary, was, by a bull of Pope Lucius III, elevated to the rank of a metropolitan cathedral.

The church is a national monument of Italy and one of the most important attractions of Sicily.

http://en.wikipedia.org/wiki/Monreale