Europe of population are Saint Petersburg, Madrid, Berlin and Rome, each having over 3 million residents. When considering the commuter belts or metropolitan areas, within the EU (for which comparable data is available) London covers the largest population, followed in order by Paris, Madrid, Barcelona, Berlin, the Ruhr area, Rome, Milan, Athens and Warsaw. "Europe" as a cultural concept is substantially derived from the shared heritage of the Roman Empire and its culture. The boundaries of Europe were historically understood as those of Christendom (or more specifically Latin Christendom), as established or defended throughout the medieval and early modern history of
History of the city religious system was clearly expansive and significant, details of its political and economic functioning remain matters of speculation. In the remnants of the Roman Empire, cities of late antiquity at first gained independence, but lost their population and their importance, starting in Roman Britain and Germania. The locus of power in the West shifted to Constantinople and to the ascendant Islamic civilization with its major cities Baghdad, Cairo, and Córdoba. From the 9th through the end of the 12th century, Constantinople, capital of the Byzantine Empire, was the largest and wealthiest city in Europe, with a population approaching 1 million.