In the summer of 1189, German crusaders marched through Hungary under the command of Frederick I, Holy Roman Emperor. Béla welcomed Frederick, and dispatched a troop to escort the crusaders across the Balkan Peninsula. At Frederick's request, Béla released his imprisoned brother, Géza, who joined the crusaders and left Hungary. Béla mediated a peace treaty between Frederick I and Isaac II, whose mutual distrust had almost caused war between the German crusaders and the Byzantines.