Frederick was now at the height of his power. His second son, Conrad, was invested with the duchy of Swabia, and the claim of Wenceslaus, king of Bohemia, to some lands which had belonged to the German king Philip was bought off. The attitude of Frederick II. (the Quarrelsome), duke of Austria, had been considered by the emperor so suspicious that during a visit paid by Frederick to Italy a war against him was begun. Compelled to return by the ill-fortune which attended this campaign, the emperor took command of his troops, seized Austria, Styria and Carinthia, and declared these territories to be immediately dependent on the Empire. In January 1237 he secured the election of his son Conrad as German king at Vienna; and in September went to Italy to prosecute the war which had broken out with the Lombards in the preceding year. Pope Gregory attempted to mediate, but the cities refused to accept the insulting terms offered by Frederick. The emperor gained a great victory over their forces at Cortenuova in November 1237; but though he met with some further successes, his failure to take Brescia in October 1238, together with the changed attitude of Gregory, turned the fortune of war. The pope had become alarmed when the emperor brought about a marriage between the heiress of Sardinia, Adelasia, and his natural son Enzio, who afterwards assumed the title of king of Sardinia. But as his warnings had been disregarded, he issued a document after the emperor's retreat from Brescia, teeming with complaints against Frederick, and followed it up by an open alliance with the Lombards, and by the excommunication of the emperor on the 20th of March 1239. A violent war of words ensued. Frederick, accused of heresy, blasphemy and other crimes, called upon all kings and princes to unite against the pope, who on his side made vigorous efforts to arouse opposition in Germany, where his emissaries, a crowd of wandering friars, were actively preaching rebellion. It was, however, impossible to find an anti-king. In Italy, Spoleto and Ancona were declared part of the imperial dominions, and Rome itself, faithful on this occasion to the pope, was threatened. A number of ecclesiastics proceeding to a council called by Gregory were captured by Enzio at the sea-fight of Meloria, and the emperor was about to undertake the siege of Rome, when the pope died (August 1241). Germany was at this time menaced by the Mongols; but Frederick contented himself with issuing directions for a campaign against them, until in 1242 he was able to pay a short visit to Germany, where he gained some support from the towns by grants of extensive privileges.