Battle of Monte Porzio: A Roman army supporting Pope Alexander III is defeated by Christian of Buch and Rainald of Dassel.

The Battle of Monte Porzio was fought on 29 May 1167 between the Holy Roman Empire and the Commune of Rome. The communal Roman army, which one historian has called the "greatest army which Rome had sent into the field in centuries", was defeated by the forces of the Emperor Frederick Barbarossa and his local allies, the Counts of Tusculum and the ruler of Albano. Comparing its effect on the city of Rome, one historian has called Monte Porzio the "Cannae of the Middle Ages".

The Commune of Rome was a semi-autonomous, citizen-led political regime established in the city of the same name, whose emergence can be included within the process of constitution of urban communes in Northern Italy. As a political-administrative entity, the Commune of Rome, with its physical headquarters on the Capitoline Hill, was made up of governing and representative bodies, justice and finance whose jurisdiction presumably included, from north to south, from the Paglia bridge in Radicofani to Ceprano and, from east to west, from Carsoli to the coastline.

Pope Alexander III, born Roland, was head of the Catholic Church and ruler of the Papal States from 7 September 1159 until his death in 1181.

Christian I (c. 1130 – 23 August 1183), sometimes Christian von Buch, was a German prelate and nobleman. He was Archbishop of Mainz and Archchancellor of Germany from 1165 until his death in 1183. He was originally elected archbishop in 1160 in a disputed election. He served the Emperor Frederick I as a diplomat in Italy on two occasions.