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
Second city of the United Kingdom remained steady around the one million mark; its central population fell like Glasgow's, but the city boundaries were extended several times in the early 20th century. Occasional claims were made for Liverpool, Birmingham and Manchester. Since World War I, and up to the beginning of the 21st century, Birmingham had been considered by many to be the second city. Based on population within actual city boundaries the City of Birmingham, the most populous local government district in Europe, is substantially larger than the City of Manchester, which is the fifth largest in the UK (2006 estimates, see List of English