Hostilities had already begun with the occupation of Diinaburg (Dvinsk) in Polish Livonia by the Swedes (July 1, 1655), and the Polish army encamped among the marshes of the Netze concluded a convention (July 25) whereby the palatinates of Posen and Kalisz placed themselves under the protection of the Swedish king.
Of these the only one of importance for navigation is the Warthe, which through the Netze is brought into communication with the Vistula.
The Vistula is connected also with the Oder by the Bromberg canal in Prussia, which links the Brahe, in the basin of the Vistula, with the Netze, a tributary of the Warta.
Lat., where the Vistula, Netze, Warthe, Oder, Spree and Havel form vast swampy lowlands (in German called Brche), which have been considerably reduced by the construction of canals and by cultivation, improvements due in large measure to Frederick the Great.
Posen belongs to the north German plain, and consists of a low plateau intersected by the beds of the Netze, the Warthe and the Obra.
By means of the Bromberger canal the Netze is joined with the Brake and then through this river with the Vistula.
Its political connexion with Prussia began in 1772, when the districts to the north of the Netze fell to the share of that power in the first partition of Poland.
The rest followed in 1793, and was united with the Netze district to form the province of South Prussia.
This engineering work, constructed in 1773-1774, by command of Frederick II., connects the Brahe with the Netze, and thus establishes communication between the Vistula, the Oder and the Elbe.