The Battle of Monte Porzio is fought on May 29, 1167, resulting in a significant victory for Holy Roman Emperor Frederick I Barbarossa against the Commune of Rome, who supported Pope Alexander III.
Pope Alexander III was forced to flee to Benevento. Frederick Barbarossa went and entered Rome, where he installed an antipope, Paschal III. Barbarossa's success short lived when a sudden outbreak of plague devastated his army, forcing him to retreat to Germany.