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 Jerusalem and the Holy Land. In Europe itself, the Church organised the Inquisition against heretics. In Spain, the Reconquista concluded with the fall of Granada in 1492, ending over seven centuries of Islamic rule in the Iberian Peninsula. In the east a resurgent Byzantine Empire recaptured Crete and Cyprus from the Muslims and reconquered the Balkans. Constantinople was the largest and wealthiest city in Europe from the 9th to the 12th centuries, with a population of approximately 400,000. The Empire was weakened following the defeat at Manzikert and was weakened considerably by the sack of Constantinople in 1204, during the