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
Religion in Europe period, Italy 84.1%:87.8%, Denmark 57.8%:62.1%. For a comprehensive study on Europe, see Mattei Dogan's "Religious Beliefs in Europe: Factors of Accelerated Decline" in "Research in the Social Scientific Study of Religion". According to new surveys about Religiosity in the European Union in 2012 by Eurobarometer, Christianity is the largest religion in the European Union accounting 72% of EU citizens. Catholics are the largest Christian group in EU, accounting for 48% EU citizens, while Protestants make up 12%, and Eastern Orthodox make up 8%, and other Christians account for 4% of the EU population. Non believer/Agnostic 16%, Atheist 7%, and Muslim