After the fall of the Roman Empire, Sicily was governed by the Ostrogoths guided by king Theodoric and then, in consequence of the wars made by Justinian to reconquer Italy, by the Byzantine Empire.
Byzantine domination was not a good period for Sicily, in fact, it was one of the remotest corners of the Empire, therefore, it was quite ignored by the sovereigns of Constantinople. Sicilian cities and Palermo in particular started decaying. The Byzantine chronicler Theophanes wrote about Byzantine Sicily as the most extreme and outcast province of the Empire.
The only enhanced city was Syracuse, still considered valuable because of its former glorious history as part of Magna Graecia. People of Palermo had to pay very high taxes to Greeks. Until last century in Palermo people used to say to naughty children ‘Viri ca vénunu i Greci!’ ([If you don’t behave], Greeks will come [to punish you]). Pope Gregory the Great made build Benedictine convents to balance the growing number of churches and convents loyal to Constantinople Patriarch. At the beginning San Giovanni degli Eremiti itself was probably one of these convents following Saint Benedict rule, dedicated to St. Hermes and it seems that this name was then mispronounced and became ‘Eremiti’.
After an initial period of transition in which Latin still was the official language, in 7th century AD Greek became the language of the whole Empire, so also of Sicily and Palermo.
During the iconoclast period (8th century AD) most of Sicily sided with the iconolaters and Palermo welcomed a lot of monks and priests from all Mediterranean countries persecuted by Emperor Leo III the Isaurian.
At the beginning of the 11th century Saracen raids were increasingly frequent and Arabs, aware of the military weakness of Constantinople Empire in Sicily, decided to conquer the island. Palermo fell almost straight away (831 AD), Syracuse on the other hand did not succumb until 878, while Catania surrendered in 900. It seems that still in 965 (year of the final fall), that is more than 100 years after Arab invasion, Rometta, a small city near Messina, was under Greek control.
Byzantine art kept influencing Sicilian architecture also during Norman domination, even if no work of the period remains. Norman Palermo was often decorated by Greek artists, who covered in wonderful mosaic the inside of Monreale Cathedral and Church of Martorana. Also the classical red domes of Martorana and San Giovanni degli Eremiti are a clear Byzantine legacy.