In the north-west, Lithuania faced constant armed incursions from the Teutonic Knights—founded after 1226 to fight and convert the pagan Baltic tribes of Prussians, Yotvingians and Lithuanians. In 1380, Jogaila concluded the secret Treaty of Dovydiškės, directed against Kęstutis. When Kęstutis discovered the plan, the Lithuanian Civil War began. He seized Vilnius, overthrew Jogaila, and pronounced himself grand duke in his place. In 1382, Jogaila raised an army from his father's vassals and confronted Kęstutis near Trakai. Kęstutis and his son Vytautas entered Jogaila's encampment for negotiations but were tricked and imprisoned in the Kreva Castle, where Kęstutis was found dead, probably murdered, a week later. Vytautas escaped to the Teutonic fortress of Marienburg and was baptised there under the name Wigand.