The Commune of Rome was briefly established in Rome in the twelfth century in opposition to the temporal power of the higher nobles and the popes. In an effort to reestablish democracy and the old Roman Republic, the revolutionaries set up a senate on the lines of the ancient one: dividing Rome into fourteen districts, each electing four senators for a total of 56 (though one source, oft repeated, gives a total of 50). These senators, the first real senators since the seventh century, for the senatorial title had become a meaningless adjunct title of nobility by then, elected as their leader Giordano Pierleoni with the title patrician, because consul was also a depreciated noble styling.
The commune declared allegiance to the Holy Roman Emperor and initiated negotiations with the newly-elected Pope Lucius II, demanding that he renounce temporal authority and take up his office with the functions of a priest. Lucius assaulted the Eternal City, but the republican defenders repulsed his army and he himself died from injuries received when a thrown stone hit him in the head. His successor, Pope Eugene III, could not be consecrated in the city, but eventually came to an agreement with the new civil authority, who had deposed Pierleoni, and returned to Rome on Christmas Day 1145, though in March 1146, he again had to leave. He returned in 1148 and excommunicated Arnold of Brescia, a political theorist who had joined the commune and who was by then its intellectual leadership. The existence of the Republic was precarious and Eugene was only installed as pope in Rome in 1152 and his successor's successor, Adrian IV, convinced Emperor Frederick Barbarossa to lead an army against the city. Arnold was arrested, tried, convicted, and executed by burning in 1155. The city was again under papal control, but the civil government was never again directly in the hands of the higher nobles or the papacy.
- Gregorovius, Ferdinand. History of the City of Rome in the Middle Ages.