Parliamentarianism in the Grand Duchy of Lithuania entered a new stage of development on 1 July 1569 when the Grand Duchy of Lithuania and the Kingdom of Poland concluded the Union of Lublin. Signed in the city of Lublin, the Act of the Union firmly enshrined the requirement to hold joint conventions. Previously, the Seimas of the Commonwealth of the Two Nations as a political institution was regarded with a degree of scepticism by historians.