After the Third Partition, the lands of Dobrzyń and Płock northeast of the Vistula river were transferred to New East Prussia, while South Prussia gained the Warsaw region of the former Masovian Voivodeship. In the southeast the Pilica river marked the border with those Lesser Polish territories that in 1795 became part of Austrian New Galicia. In the southwest it bordered on the Prussian Silesia Province and New Silesia, a smaller province including the former Duchy of Siewierz, which was administered from South Prussia.