Moscow is the largest city entirely on the European continent. It has 13.2 million people in the city limits, and 17.8 million in the urban area. One of the nicknames for Moscow is the 'Third Rome'. After the capture of Constantinople by the Ottoman Empire in 1453, the Grand Duchy of Moscow started to see itself as defenders of the Orthodox Faith. This was central to Byzantine identity to distinguish themselves from the Barbarians, from the North-West and from the East, who had overthrown the previous Empires. Mehmed II, conqueror of Constantinople declared himself Kayser-i-Rum, "Caesar of Rome". Ferdinand and Isabella who built up the Spanish Empire, bought the titles and imperial rights from the heir of the last Byzantine Emperor. The Barbarians became the Emperors. The Emperors became the Barbarians. And repeat.