 The combination of imperial power and a key location at the crossing point between the continents of Europe and Asia, and later Africa and others regions, played an important role in terms of commerce, culture, diplomacy, and strategy.It was the center of the Greek world and, for most of the Byzantine period, the largest city in Europe.Constantine's conversion to Christianity, in 312, had set the Roman Empire towards Christianization, and in 381, during the reign of Theodosius I, the official state religion of the Roman Empire became Christianity, turning Constantinople into a thriving religious center.