In the development of civilization, an often overlooked contributor was the Roman-Greek empire of Byzantium. The influences of Byzantium affected Western art, architecture, military technology, philosophy and even medicine. Justinian the Serbian peasant and Byzantine Tsar in 535 AD onwards, initiated a series of wars to reclaim Western Roman territory which devastated Italy and North Africa, weakening both areas for generations. In the Byzantine mind, the Western Roman empire, which had splintered into 3 Germanic kingdoms and various petty Lordships; belonged to the Eastern Roman empire.
The Moslems plundered Byzantium both literally and figuratively, and it is from the Eastern Roman empire that all of the Islamic architecture is derived. Indeed Byzantine Christian slaves and dhimmis were vital in the management of various Caliphates, the teaching of Greek and Roman literature and learning to Moslems; the translation of essential ideas and works ranging from astronomy to medicaments; and of course the architecting of sundry Mosques. The Grand Mosque in Cordoba uses the columns, arches and layout of various temples, public buildings and bath houses found in Constantinople.
Eastern Rome before the time of the Moslem invasions had become rich. But it also had become mystical, bureaucratic, ossified, and out of date. It was rigid. The fact that remnants of the Eastern Roman empire survived until 1453 and the Moslem eradication of Constantinople [40.000 killed, 30.000 enslaved]; is a remarkable testimony, however, to its former power, importance and organization. What Eastern Rome needed was the Western 'renaissance' which occurred after the Western Roman empire thankfully went out of business. Both empires outlived their usefulness and their utility, especially regarding the lives of ordinary people, and the further development of civilization including its spiritual component.
An excellent one volume study of Byzantium is by Julius Norwich. Though in need of repair the Moslem destruction of this civilization was a tragedy.
“Byzantine's collapse was for many reasons, an inevitability. Nevertheless its destruction is one of the greatest tragedies in history. The Turkish takeover of Constantinople and the destruction of a noble, intelligent and complicated culture did nothing to advance civilisation. In the place of Greek and Roman learning, there was erected a primitive, expansive and aggressive Islamic cult and empire – shut off from inquiry, science and spiritual tolerance and dedicated to imperialism. We see the results today in the failed Islamic states which gird the globe from North Africa to Pakistan. This might have been Europe's fate as well - if not for Byzantium.”