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Ducatus Ultradunensis (Latin for Transdunian Duchy; Duna is an ancient name of the Daugava River) was the name given to part of Livonia by Zygmunt II August in 1566, after the dissolution of the Livonian Confederation. Covering what is now Vidzeme and Latgale in Latvia and southern Estonia, it was a province of Lithuania until 1569, and a condominium of Lithuania and Poland until ~1621, when the larger part of the Duchy was ceded to Sweden. The southeastern part of the Duchy (now Latgale) remained part of the Polish-Lithuanian Commonwealth until it was joined to the Russian Empire in 1772, and was known as Polish Livonia or Inflanty (a corruption of the German for Livonia, Livland).
