from Wikipedia Milan:
Milan (Italian: Milano; Western Lombard: Milan (listen)) is one of the largest cities in Italy, located in the plains of Lombardy. The municipality (Comune di Milano) has a population of 1.3 million. The Milan metropolitan area, depending on the specific definition, has a population ranging from 2.9 to 7.4 million. The municipal border covers a relatively small area (about one-eighth of that of Rome) because of the historical development of high density centres in agriculturally rich Lombardy.
Milan is renowned as one of the world capitals of design and fashion. The English word milliner is derived from the name of the city. The Lombard metropolis is famous for its fashion houses and shops (such as along via Montenapoleone) and the Galleria Vittorio Emanuele in the Piazza Duomo (reputed to be the world's oldest shopping mall). The city hosted the World Exposition in 1906 and will host the Universal Expo in 2015. Inhabitants of Milan are referred to as "Milanese" (Italian: Milanesi or informally Meneghini or Ambrosiani).
The Olona river, the Lambro river and the Seveso creek run through Milan. Olona and Seveso run mostly underground.