Complex sentence: Monzan independence lasted until 1185 when Barbarossa ended the conflict with the Lombard League with the peace of Constance, and had to leave the city of Milan to self-rule that the subjects again and takes possession of the Treasury of the Cathedral.
Split into simpler sentences: Monzan independence lasted until 1185 when Barbarossa ended the conflict with the Lombard League with the peace of Constance. He allowed the city of Milan to self-rule its subjects again, while taking possession of the Treasury of the Cathedral.