The Byzantines had possession of Sicily off and on for hundreds of years, until they finally lost it forever during the reign of Empress Zoe and her three husbands in the 11th century. Following the Byzantines came the Moslems from North Africa, who held it for a few decades before Norman mercenaries wandered down into Italy and decided to stay.
Those Norman mercenaries included the infamous (for the Byzantines) Robert Guiscard and several of his many (at least 11) brothers, with the youngest brother to make it to southern Italy being Roger. Robert Guiscard was a soldier whose strength was in conquering, not ruling. He eventually earned the title of Duke of Apulia and made an impressive effort to become the emperor in Constantinople. Generously, he gave the territory he had won in Sicily to brother Roger. In time, Roger pushed the Moslem emirs off the rest of the island and earned the title of Count of Sicily.
The art in Sicily during the time of Roger and his descendants/successors demonstrated their deep admiration of the Eastern Roman Empire. The mosaics at Monreale, the Palatine Chapel and Cefalu all bear the unmistakable mark of Byzantine culture with their looming Christ Pantocrators in the church apses.
Even more interesting is how the Norman Sicilian counts (and later kings) were depicted in the mosaics of their churches. Above you can see an image of the Byzantine Emperor Constantine Monomachos who is depicted in the typical 11th century attire for an emperor with its distinctive sash and belt (lorum), and the red shoes worn by emperors. Below are images of Norman Sicilian rulers as depicted in the mosaics of their churches in similar clothing.
William II at Monreale:
Even some of the angels at Monreale were attired as Byzantines:
And another image of William II, at the dedication of Monreale.
It is clear from these mosaics that the rulers of this great medieval island kingdom admired Byzantine culture and used its symbols of wealth and power to demonstrate their own strength. Unfortunately, the Norman rulers only lasted a few years after the death of William II, their rule ending with the overthrow of young William III by the Holy Roman Emperor Henry VI in 1194, a mere ten years before the devastating events of 1204 by the Fourth Crusade.
The Byzantine/Eastern Roman Empire had passed its peak by the late 12th century when Monreale was built but, as demonstrated by these magnificent mosaics, still represented the highest level of culture and sophistication in Europe and the one its rulers found most worthy of imitation.