John of Brienne had received the crown of Jerusalem as his wife's dowry, and it was destined that the marriage of his daughter should restore the Holy City to the Christians. The emperor Frederick II. had often vowed in the most solemn manner to lead his armies into Palestine, and had as often broken his oath. At length it was proposed to him that he should wed Violante, the beautiful heiress of the Syrian kingdom; and it was easily stipulated that John of Brienne should give up his rights on Palestine to his daughter's husband. Frederic eagerly caught at the idea. By the intervention of the Pope the treaty was concluded between the king and the emperor; and Violante, having been brought to Europe, was espoused by her imperial lover.[830] Many causes combined to delay the new crusade, though it was preached by two succeeding popes with all the zeal and promises that had led to those that went before. France and Italy remained occupied entirely by intestine dissensions; but England showed great zeal, and sent sixty thousand men at arms to the field.[831] The emperor collected together immense forces, and proceeded to Brundusium; but there, being taken ill of a pestilential disease which had swept away many of his soldiers, he was obliged to return after having put to sea. Gregory IX. was now in the papal chair; and--wroth with the emperor for many a contemptuous mark of disobedience to the ecclesiastical authority--he now excommunicated him for coming back, however necessary the measure. Frederic was angry, though not frightened; and, after having exculpated himself to Europe by a public letter,[832] he sent his soldiers to plunder the Pope's territories while he recovered his health. At length, in 1228, he set sail from Brundusium, still burdened with the papal censure, which he was too much accustomed to bear to feel as any oppressive load. He arrived without difficulty at Acre; but all men wondered that so great an enterprise should be undertaken with so small a force as that which could be contained in twenty galleys; and it soon appeared that Frederic had long been negotiating with Camel, Sultaun of Egypt, who, fearful of the active and ambitious spirit of his brother Cohr Eddin,[833] had entered into a private treaty with the German monarch.