Insubria is a historical-geographical region which corresponds to the area inhabited in Classical antiquity by the Insubres; the name can also refer to the Duchy of Milan (1395–1810). For several centuries this name stood for an area stretching approximately between the Adda river in the east and the Sesia river in the west, and between the San Gottardo Pass in the north and the Po river in the south, thus it was a synonym of the Milan region and the surrounding countryside corresponding with Lombardy in modern Italy. Polybius claims the Insubres founded the city of Milan around 600 BC. They were a Celtic or Ligurian people which dwelt in the 4th–5th century BC in the area of pre-Alpine lakes (the Italian Lakes) and Milan. The name Insubres is visible in the middle portion of the Tabula Peutingeriana. The symbol of Insubria (when conceived as the Duchy of Milan) is the Milanese Ducal flag, the Visconti child-swallowing serpent quartered with the Imperial eagle. For further details, see the Duchy of Milan. At present, the meaning of the term Insubria is perceived as more restricted, as it indicates the territory of the cross-boundary cooperation community Regio Insubrica, which was set up in 1995 by the Italian provinces of Varese, Como, Verbano-Cusio-Ossola together with the Swiss Canton Ticino: that is to say, the lakes area between Italy and Switzerland where the Italian language is spoken. The Regio Insubrica was recently extended to the territories of the provinces of Novara and Lecco. It is a Euroregion (complying with the Madrid Agreement by the Council of Europe) which promotes cross-boundary cooperation in the Italian-Swiss region of the three pre-Alpine lakes (i.e., Lake Como, Lake Lugano and Lake Maggiore). From an ethnolinguistic viewpoint, Insubria also comprises the provinces of Novara, Lecco, Milan, and Lodi, that is, those areas in which the Western Lombard or Insubrian variety of Lombard language is spoken and which correspond to the territory of the former Duchy of Milan until its takeover by the Habsburg Empire as a result of the Treaty of Baden in 1714 or, better said, of the Treaty of Campo Formio (1797), which marks the end of the first Austrian domination.