The same year, 1237, Frederick approached Mantua, and thus giving courage to the Ghibelline party, made them triumph over the Guelfs, who had, till then, the ascendant in that city; he was joined there by ten thousand Saracens, whom he summoned from Apulia, and afterwards advanced into the Cremonese territory to attack the confederate army of the Guelfs, commanded by the consuls of Milan, who knew no other art of war but the bravery evinced in battle. Frederick was a more able captain; by manœuvring between Brescia and Cremona, he drew the Milanese beyond the Oglio, and finally succeeded, as they believed the campaign finished, in placing himself between them and their country at Cortenuova near Crema. The Guelfs, although thus cut off from retreat, boldly accepted battle on the 27th of November, 1237, and long disputed the victory. Their defeat was only the more bloody; it cost them ten thousand men killed or taken prisoners, with the loss of the _carroccio_. The fugitives followed during the night the course of the Oglio to enter the Bergamasque Mountains; they would all, however, have fallen into the hands of the Ghibellines, if Pagan della Torre, the lord of Valsassina, and a Guelf noble, had not hastened to their assistance, opened the defiles covered by his fortresses, and brought them thus safely to Milan. The citizens of this town never forgot so important a service; and they contracted with the house of della Torre an alliance which subsequently proved dangerous to their freedom. The defeat of the Guelfs at Cortenuova alarmed the towns of Lombardy, the greater number of which detached themselves from Milan. Frederick, entering Piedmont the following year, gave preponderance to the Ghibelline party in the cities of Turin, Asti, Novara, Alexandria, and several others. The constitution was not changed when the power in council passed from one party to another; but the emperor generally reckoned his partisans among the nobility, while the people were devoted to the church; accordingly, the triumph of the aristocracy generally accompanied that of the Ghibelline party. Four cities only, Milan, Brescia, Piacenza, and Bologna, remained at the end of the year opposed to the imperial power. Frederick began his attack on them by laying siege to Brescia; but the Brescians dared to face the storm; they supported, during sixty-eight days, the repeated attacks of the emperor, rendered all his efforts fruitless, and forced him at last to raise the siege with an army weakened and discouraged. POPE AGAINST EMPEROR [Sidenote: [1238-1243 A.D.]]