Breisgau (brĪsˈgou) [key], region, Baden-Württemburg, SW Germany, including the Rhine plain and the western slopes of the Black Forest. Freiburg is the chief city. After the extinction (1218) of the first house of Zähringen, it was divided among various heirs. Most of it passed to the Hapsburgs in 1368. France held the region at various times in the 17th–18th cent. In 1805 the Breisgau was divided between Baden and Württemburg; the latter gave its share to Baden in 1810.