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
Europe (later Kingdom and Empire), and the Duchy of Croatia (later Kingdom of Croatia). To the East, the Kievan Rus expanded from its capital in Kiev to become the largest state in Europe by the 10th century. In 988, Vladimir the Great adopted Orthodox Christianity as the religion of state. Further East, Volga Bulgaria became an Islamic state in the 10th century, but was eventually absorbed into Russia several centuries later. The period between the year 1000 and 1300 is known as the High Middle Ages, during which the population of Europe experienced significant growth, culminating in the Renaissance of the