What is "insubria"

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 countryside areas gravitating towards it.