During the last six years of his life King Sverre had a continual war with the Baglers. His first encounter with them was in Saltoe Sound, in Viken. After an indecisive battle there he returned with his ships to Bergen and proceeded to Nidaros, where he spent the winter 1196-97. The Baglers meanwhile summoned the Borgar-Thing, where Inge was proclaimed king. The next year King Sverre gathered a strong force and proceeded to Viken, and defeated the Baglers at Oslo, July 26, 1197. After the battle Bishop Nicholas sent a messenger to King Sverre that he was willing to make peace; but Sverre, who knew how little Bishop Nicholas was to be depended upon, sent word back that he would only treat with him if he would come in person. Bishop Nicholas did not go to meet the king, but instead hastened with the chiefs and the remaining force of the Baglers overland to Nidaros, where the wooden citadel (blockhouse) "Zion" fell into their hands by the treason of its commander, Thorstein Kugad. They destroyed some of the fortifications and burned a number of Sverre's ships and took possession of the remainder. A part of the Bagler force went aboard the captured ships, and sailed southward under the leadership of Sigurd Jarlson. The others returned to Viken the same way they had come. King Sverre spent the following winter in Bergen, and in the spring (1198) sailed north and met the Baglers in battle at Thorsberg, near the mouth of the Throndhjem Fjord. After a hard fight the Birchlegs were defeated with great loss. The king then hastened back to Bergen, which had in the meantime been occupied by the Bagler chief Sigurd Jarlson. The latter, however, having, by a clever trick of one of the Birchlegs, been led to believe that King Sverre was approaching with a much superior force, left the town before Sverre arrived.