(Latin, Ducatus Ultradunensis), the part of medieval Livonia seized by the Polish and Lithuanian feudal lords during the Livonian War of 1558–83. The duchy consisted of the Latvian lands north of the Western Dvina (Daugava) with the exception of Riga and southern Estonia. Joined to the Grand Duchy of Lithuania by the treaties of 1561 and 1566, the Trans-Dvina Duchy became a part of the Polish-Lithuanian Commonwealth after the Union of Lublin of 1569. The duchy’s political structure was consolidated after the Livonian War. It was headed by an administrator or a governor appointed by the king of Poland; but in fact the duchy was ruled by the German knights, who retained ownership of more than half of the land together with judicial and police power over the peasants. As a result of the long Polish-Swedish war that began in 1600, the duchy gradu-ally fell apart, and its territory, except for Latgalia, passed to Sweden in 1629.
REFERENCESDoroshenko, V. V. Ocherki agrarnoi istorii Latvii v XVI v. Riga, 1960. Pages 58–76.
Tarvel, E. “Stosunek prawnopaństwowy Inflant do Rzeczypospolitej oraz ich ustroj administracyjny w 1. 1561–1621.” Zapiski historycwe, 1969, vol. 34, no. 1, pp. 49–77.