Frederick, returning hastily from a campaign against the Pope, found his castles captured, Milan re-risen defiant from her ashes, and all North Italy armed against him. The Emperor was not equal to this new situation. His former triumph had, in fact, only been achieved by the aid of a part of the cities themselves, and his German levies, diminished by fighting and pestilence, were powerless to contend with a vast hostile combination of all together. His army and his very person were in utmost peril. There was one way only of salvation for him—retreat. In a manner very different to the majesty of his coming, with furtive haste, unknown even to his allies, he stole back to Germany early in 1168.
Six years passed before the Emperor felt himself strong enough to confront his rebellious vassals again. In his prolonged absence the Lombard League had acquired mighty strength. Milan had arisen from her chastening of shame and sorrow stronger and more honourable than before. Renouncing her old vexatious claims upon her smaller neighbours, she now contented herself with the dignity of leadership among the Communes. The League gathered itself together to meet the new onslaught of Barbarossa, and though he spread terror and desolation throughout the land, his effort to subdue the steady resistance of the cities was fruitless. His purpose was contrary to the laws of nature, and the stars in their courses fought against him. Pavia, Como and the Marquis of Montferrat supported him alone of all North Italy. In May 1176, impatient to strike a crushing blow against the rebels, Frederick was marching with new reinforcements from Germany to join his Lombard allies when, a few miles from Milan, between Busto Arsizio and Legnano, he encountered the Milanese army, which had come forth with the Sacred Car in its midst to stay his progress. A great battle took place. Driven back at first by the Teuton cavalry, the Republican soldiers, who had taken a desperate vow to conquer or to die, rallied around the Caroccio, and fought with such obstinate courage that they beat back every assault of the foe, and at last, with a sudden rush, utterly routed them and drove them into flight. The slain, the captives, and the fugitives drowned in the Ticino could not be numbered. The monarch’s treasure-chest fell into the hands of the victors, and a more precious booty still, his shield, his banner and his lance. His very person was missing after the battle, and the Empress, waiting in the Castle of Baradello, clothed herself in black and mourned him for dead. He had, however, escaped in safety, and a few days later made his way to Pavia.