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
Christianity in Europe Christians were part of the Protestant tradition. Russia is the largest Christian country in Europe by population, followed by Germany and Italy. Since at least the legalization of Christianity by the Roman Emperor Constantine in the 4th century, Europe has been an important centre of Christian culture, even though the religion was inherited from Africa and the Middle East and important Christian communities have thrived outside Europe such as Oriental Orthodoxy and the Church of the East since the time of Christ. Christian culture has been an important force in Western civilization, influencing the course of philosophy, art, and science.