GREGORY IX., Cardinal Ugolino, bishop of Ostia, a native of Anagni, and a relative of Innocent lit, whose haughty principles concerning the papal prerogative he inherited, succeeded Honorius III in March 1227. He insisted on Frederick II. setting off on a crusade, and as the emperor delayed on the pretext of illness, the pope excom municated him. Frederick however set off for Palestine, where he concluded a truce with the Sultan of Egypt, and then returned to Europe, where his dominions of Apulia had been invaded by the papal forces. After his landing he had an interview with Gregory, who relieved him from the and Frederick afterwards assisted the pope against the people of Rome, who were in a state of Insurrection, and had driven him from their city. Frederick afterwards discovering that the pope was tampering with the Lombard cities, who were at war with the emperor, came again to an open rupture with him ; and on Palm Sunday of the year 1239 Gregory again excom municated him, released his subjects from their allegiance, and preached a crusade against him. The emperor replied by a spirited manifesto
in his own justification, which was written by his learned chancellor Pietro dells Vigne, and copies of it were sent to the various courts of Europe. The war continued during that and the following year in Italy between Frederick and his Ghibeline partisans on one side, and the Guelphs, with the pope at their head, on the other. Frederick took Benevento and threatened Rome, where he had many partisans. The pope having convoked a council in 1241, the emperor arrested all the prelates who were on their way to Rome by land, while his fleet, joined with his allies the Pisans, attacked and defeated a Genoese squadron, on board of which were many bishops and abbots from Franco and other parts, who were taken prisoners. In August of that year Gregory died, after a stormy pontificate of nearly fourteen years , and was succeeded by Celestine IV.