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
Trams in Europe (Voronezh). Saint Petersburg's tramway network is largest in Europe, once had been the largest in the world, but has yielded its position to Melbourne. Tram in Molochne (Crimea, Ukraine) – is the smallest tram system in the world. Trams in Europe Europe has an extensive number of tramway networks. Some of these networks have been upgraded to light rail standards, called "Stadtbahn" in Germany, premetros in Belgium, "" in the Netherlands, and fast trams in some other countries. All the former communist countries of Central and Eastern Europe, excluding Lithuania, the Republic of Macedonia, Montenegro, Moldova and Slovenia, have extensive