The Battle of Storsjön (Slaget på Storsjöns is) was fought during 1178 outside Sunne, in Jämtland province, Sweden. The battle was won by the Birkebeiner army of King Sverre of Norway. The battle was conducted near Lake Storsjön, which was then covered with ice. Due to darkness, Sverre and his troops pulled away while local peasants fought against each other. When dawn came, the Birkebeiner forces attacked and won a victory. As a consequences of this defeat, Jämtland was incorporated into Norway until it was ceded to Sweden in 1645.