Milan is a city in northern Italy, capital of Lombardy, and the second-most populous city in Italy after Rome, with the city proper having a population of 1,372,810 while its metropolitan city has a population of 3,245,308. Its continuously built-up urban area (that stretches beyond the boundaries of the Metropolitan City of Milan) has a population estimated to be about 5,270,000 over 1,891 square kilometres (730 square miles). The wider Milan metropolitan area, known as Greater Milan, is a polycentric metropolitan region that extends over central Lombardy and eastern Piedmont and which counts an estimated total population of 7.5 million, making it by far the largest metropolitan area in Italy and the 54th largest in the world. Milan served as capital of the Western Roman Empire from 286 to 402 and the Duchy of Milan during the medieval period and early modern age. Milan is considered a leading alpha global city, with strengths in the field of the art, commerce, design, education, entertainment, fashion, finance, healthcare, media, services, research and tourism. Its business district hosts Italy's stock exchange and the headquarters of national and international banks and companies. In terms of GDP, it has the third-largest economy among European cities after Paris and London, but the fastest in growth among the three, and is the wealthiest among European non-capital cities. Milan is considered part of the Blue Banana and one of the "Four Motors for Europe".