Battle of Monte Porzio The Battle of Monte Porzio ( also called the Battle of Tusculum ) 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 been called Monte Porzio the " Cannae of the Middle Ages " . The site of the battle was the field between a small hill and the walls of the city of Tusculum , at a place called " Prataporci " , about 25 km southeast of Rome . In his universal chronicle , the " Chronica Universalis " , the contemporary writer Sicard of Cremona describes the site of battle as " near Monte Porzio " ( " apud Montem Portium " ) . The Battle of Monte Porzio is part of the long struggle between the Italian city - states and the Holy Roman Empire . In 1166 , Barbarossa set out on an expedition to Italy with the intent of deposing the anti - imperialist Pope Alexander III and setting up his own antipope , Paschal III . He also sent two eminent prelates of the Empire , Archbishop Rainald of Cologne and Archbishop Christian of Mainz , commanding armies into Latium ( the region around Rome ) to subdue those city - states still opposing the power of the emperor . On 18 May , Rainald took Civitavecchia and then moved into the friendly city of Tusculum , possibly at the suggestion of Count Raino , an imperialist . The communal Roman army had been harassing Tusculum , a longtime rival . Pope Alexander , knowing that Barbarossa was likely to come to Raino ' s assistance , urged the Romans to abstain from attacking his city . It did not work : when the consul ( leader ) of the Roman commune learned of the arrival of Rainald at Tusculum , he sent an army to besiege the archbishop in the city . With the Roman army approaching , Count Raino and Archbishop Rainald sent word to Christian , who was away besieging Ancona on the coast , to come to their relief . Within Christian ' s army were the forces commanded by Bishop Alexander II of Liège , and Count Robert III of Loritello . The total number of troops Christian was leading was about 1 , 300 , which , according to Otto of Sankt Blasien , was a combination of 500 knights ( " milites " in contemporary Latin ) and 800 " caesarianos " ( imperial troops ) . Otto places 300 men inside Tusculum . Other chroniclers claimed the Christian had with him 1 , 000 cavalry and some Brabantine mercenaries . The lowest estimate of Christian ' s forces put it at 500 men . Christian encamped his army beside the hill and rested for a day while trying to negotiate a resolution . The communal Roman army refused Christian ' s diplomatic overtures and instead attacked with their whole force , numbering 10 , 000 poorly - armed men , on Whitsunday . The name of the leader of the Roman force has not been preserved , but it may have been Oddo Frangipani . The imperial forces were gravely outnumbered , but they were more disciplined and better armed . The Brabantines were quickly routed , but the cavalry from Rainald ' s city , Cologne , withstood the charge of the Roman infantry . Two sallies from Tusculum divided the Romans : one hitting their flank and one running through the centre . As the Roman cavalry fled the field , the Brabantines descended on the Roman camp . Only a third of the Roman army had made it inside Rome ' s walls before nightfall . Thousands were eventually taken prisoner and sent to Viterbo ( including a son of Oddo Frangipani ) , and more were left dead on the field and the road . The pope and Oddo took refuge in the Colosseum ( which at the time was fortified like a castle ) and called in reinforcements . The city prepared for a siege . Later the pope fled to the city of Benevento and the Emperor entered Rome . The imperial army , however , was hard hit by a wave of either malaria or plague , and Barbarossa withdrew his forces to Germany .