The secret of Byzantium's success and staying power is surely related to its component elements: ancient Greek culture and pagan energy, preserved in its original language and transmitted through well-organised educational methods; Roman law, administrative strength and military reach and confidence, and, finally, Christian faith in its eastern form, which remained very close to the stories of Jesus's life on earth. When combined, these formed an "inner Greek fire". Greek fire itself was a combustible weapon produced from a mixture of naptha and other substances, which burned even on contact with water. The Byzantines projected it under pressure through siphons against enemy ships, threw it on to city walls under siege and against enemy troops, who fled at the sight. This spiritual version of Greek fire formed the kernel of Byzantine civilisation and stoked the survival of the empire for more than 1,100 years.

Under its inspiration many features of Byzantium assisted in the process, notably the growth of Constantinople as an international market which linked the landmass of Russia with the Mediterranean world. Byzantine emperors also issued a reliable gold coinage with their own names and images, which circulated widely and served as imperial propaganda. They encouraged people of many different ethnic origins to come and trade in Byzantium, creating a multicultural society. Jews, Armenians, Arabs, Slavs were all attracted to Byzantium, not only to the capital but also to the numerous fairs held in provincial cities, often on the feast day of the local Christian saint. They recruited foreign forces, such as the Varangians from Scandinavia, Russia and Anglo-Saxon England, to guard the imperial court and fight in imperial armies. And the development of a sophisticated diplomatic corps sustained Byzantine imperial ideology throughout the medieval world and beyond, extending as far east as China and west to Muslim Spain.

Byzantium also benefited from having a particularly grand capital city, Constantinople. At its height, first in the 6th century and then in the 12th, the "city of Constantine" may have contained as many as 500,000 people, vastly bigger than any western medieval city. The accounts of visitors all make clear that its sheer size and fortifications, its harbours and markets, its imperial court, public buildings and huge churches greatly impressed travellers. As the 10th-century Russian ambassadors reported when they entered the church of Holy Wisdom, Hagia Sophia: "We knew not whether we were in heaven or on earth ... We only know that God dwells there among men, and their service is fairer than the ceremonies of other nations." Visitors assumed, quite correctly, that such grandeur required immense wealth, which the emperors generated through taxation on land and commerce. A regular tax-raising capacity was another feature unfamiliar to other medieval states. In addition, the city provided education from the lowest to the highest levels, which was essential to a career in the civilian bureaucracy. To gain a paid position required considerable knowledge of ancient Greek rhetoric and culture. The epics of Homer, the plays of ancient Greek dramatists, the speeches of Pericles and Demosthenes as well as the writings of Plato, Aristotle, Hippocrates, Archimedes and Euclid were all studied and copied in Byzantium and thus preserved.