All information here so far is sourced from Matthew Paris:
100,000 men in Imperial Army – plus Saracen mercenaries
60,000 in Milanese army
The two forces separated by river Oglio
The Milanese attacked first – destroying the Saracens – were the archers forming a covering front for the Imperial army?
Frederick counter-attacked with his nobles was this a mounted cavalry charge?
General melee with numerous assaults on each side proceeded.
Matthew Paris also records another version of events as told in the Emperor’s letter to Richard, Earl of Cornwall. In this version, which is much more detailed and interesting, the Imperial forces had been trying to induce the Milanese to take part in an open battle, presumably knowing that their superior forces would probably overcome the Milanese. Frederick recounts how the Milanese were summoned to support Brescia and provide a garrison for it. They were caught by the Imperial forces in a bend of the river Oglio. The Milanese tried to march back to their city, but Frederick marched the vanguard of his army along the river to reach the fords and bridges that the Milanese would have to use. The Milanese were caught in confusion and fled in panic from the advancing Imperial forces. They retreated towards Nouva Croce, and had sent their carrochium ahead of them. Frederick mentions that a force of auxillary troops (what were these forces – Saracen archers or more lightly armed foot and cavalry?) had gone ahead and had caused destruction and confusion amongst the retreating Milanese. At the castle of Nouva Croce the carrochium was fortified behind trenches outside the castle and it was here that the Milanese made their stand with a strong force of knights and foot soldiers. The brave Imperial forces crossed the trenches, in what sounds like almost WWI conditions, they went over the top of the trenches and nearly reached the flagpole of the Milanese war-wagon. The fighting ended with nightfall, and, sleeping in his armour, Frederick was hopeful of finishing the Milanese off on the next day. They found the field empty. The wagon had been left outside the walls of Nuova Croce with the cross at the top of the flagpole cut off. However, they Milanese in their retreat had abandoned the cross section as well. The garrison of Nuova Croce surrendered and Frederick proceeded to besiege Milan.
Milanese fell back to the protection of their city. Three thousand men of rank were taken prisoner and numerous common soldiers killed rather than taken prisoner.
It seems that the Emperor organised an ambush of the leaders of the Milanese army as it retreated, and seized the carrochium, the city’s podesta (who was the son of the Doge of Venice), and numerous other nobles were killed including the Bishop of Milan.
The city was then besieged. Matthew describes bridges being destroyed and roads blocked so that it seems that this was a general encirclement of the city to try to block off access. The Emperor must therefore have had a larger force at his disposable than he would in 1247 at Parma.
According to Matthew Paris the Milanese attempted a sally to break the siege with 50,000 men, but gave up when one of their commanders counselled against. He warned that Frederick’s vengeance against them would be more terrible if they took aggressive action against Frederick, rather than defending themselves in their city.
The siege had to be raised however, when word came of the rebellion of the Duke of Austria. The Milanese took back the castles Frederick had fortified around their city and slaughtered the garrisons.