The Great Northern War began on 12 February 1700. The King of Poland and Elector of Saxony, Augustus II, crossed the Düna river with his Saxon troops and besieged the city of Riga in Swedish Livonia. Riga was defended by Governor-General Erik Dahlbergh. Simultaneously, King Frederick IV of Denmark and his Danish troops invaded Holstein-Gottorp and laid siege to Tönning on March.