During the reign of Otho, while the political field was divided between him and the young Suabian prince, the disputed imperial authority had no power to harm, and Milan was free to resume the interrupted process of development and expansion. As before, this process was not a peaceful one. The subsidence of the Teutonic flood had left behind bitter dregs in Lombardy in the shape of new causes of feud and animosity between individual Communes. Relieved from the pressure of Frederick’s tyranny, the cities readjusted themselves on the lines of their former divisions. The Lombard League broke up into warring elements, and the restless land fermented with a cruel internecine strife. [Illustration: ATRIUM OF ST. AMBROGIO] But when, some years later, Frederick II., grown to manhood, had cast off the bondage in which the Pope had fettered his youth, and seated on the imperial throne proved himself indeed _the third blast of Suabia_, heir in spirit as in blood of his mighty grandsire, the Communes proved true to one another, and to the newly threatened cause of freedom, and the great Lombard League, with Milan at its head, sprang to life again to face the tyrant. During the long and desolating wars which Frederick’s ambition inflicted upon North Italy, Milan steadfastly fought against him, even when most of her fellows had been induced by fear or self-interest to desert the good cause. Late in 1237 her army, which had marched to the aid of the Brescians, was surprised by the imperial host at Cortenuova and suffered a crushing defeat. Multitudes of her soldiers perished, and the Sacred Car itself, stuck fast in morasses, had to be abandoned in the retreat. Its defenders were able, however, to save the Cross and Banner, and break the car to pieces. Frederick’s exultation over these fragments, upon which he bound the captive Podestà of Milan, Pietro Tiepolo, son of the Doge of Venice, and dragged him, in imitation of a Roman triumph, through the streets of Cremona, is a measure of the importance which he attached to his victory over the Lombard city. With the defeat of Cortenuova the cause of the Communes seemed lost. All trembled beneath the heel of the conqueror, save Milan and the ‘lioness’ Brescia, and one or two others. To the Emperor’s summons to surrender at discretion the Milanese returned messages of defiance. They had the support of the Pope, whose emissaries, the mendicant friars, mingled everywhere with the masses of the people, exhorting them to resistance. In 1239, Gregory proclaimed a crusade against the oppressor, whose destruction thus became a sacred obligation upon the faithful. The Cross and the Sceptre, irreconcilable emblems, now confronted each other with a clear and definite issue.