Venta River
Several parts of the Courish area did not belong to the Duchy. The Order of Livonia had already loaned the Grobiņa district (on the coast of Baltic Sea) to the Duke of Prussia. Another district, the Bishopric of Piltene, also called the "Bishopric of Courland" (on the Venta River in western Courland), belonged to Magnus, son of the king of Denmark. He promised to transfer it to the Duchy of Courland after his death, but this plan failed and only later did Wilhelm Kettler regain this district.