The Diet of Porvoo (Finnish: Porvoon maapäivät, or unhistorically Porvoon valtiopäivät;[a] Swedish: Borgå lantdag;[b] Russian: Боргоский сейм), was the summoned legislative assembly to establish the Grand Duchy of Finland in 1809 and the heir of the powers of the Swedish Riksdag of the Estates. The session of the Diet lasted from March to July 1809.
During the Finnish War between Sweden and Russia, the four Estates of Russian-occupied Finland (nobility, clergy, burghers and peasants) were assembled in Porvoo (Borgå) by Tsar Alexander I, the new Grand Prince of Finland, between 25 March and 19 July 1809.
Finnish historians disagree on whether the Diet of Porvoo was the first meeting of The Estates in the history of Finland or a traditional landtag where the eight easternmost regions of Sweden were transferred under the authority of the Emperor of Russia. According to the interpretation of the Finnish constitution born later in the 19th century, the state of Finland was born at the Diet of Porvoo. The historian Henrika Tandefelt claims that the Porvoo Diet could not have been a riksdag ("meeting of the state") as there was no state to speak of at the time.
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