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al structure—that of a semi-federal, semi-confederal aristocratic republic—was formed in 1569 by the Union of Lublin, which united the Crown of the Polish Kingdom and the Grand Duchy of Lithuania, and lasted in this form until the adoption of the Constitution of May 3, 1791. The Commonwealth covered not only the territories of what is now Poland and Lithuania, but also the entire territory of Belarus and Latvia, large parts of Ukraine and Estonia, and part of present-day western Russia (Smolensk and Kaliningrad oblasts). Originally the official languages of the Commonwealth were Polish and Latin (in the Kingdom of Poland) and Ruthenian and Lithuanian (in the Grand Duchy of Lithuania). The creation of the Commonwealth by the Union of Lublin in 1569 was one of the signal achievements of Sigismund II Augustus, last monarch of the Jagiellon dynasty, in an effort to preserve the monarchy by adopting elective monarchy. His death in 1572 was followed by a three-year interregnum during which adjustments were made to the constitutional system that effectively increased the power of the nobility and established a truly elective monarchy.