After the failure of the crusade, John travelled throughout Europe seeking assistance, but found support only from Frederick, who then married John and Maria's daughter Isabella II in 1225. The next year, Isabella died giving birth to their son Conrad IV, who succeeded his mother to the throne although he never appeared in the east. Frederick had reneged on his promise to lead the Fifth Crusade, but was now eager to cement his claim to the throne through Conrad. There were also plans to join with al-Kamil in attacking al-Mu'azzam in Damascus, an alliance which had been discussed with Egyptian envoys in Italy. But after continually delaying his departure for the Holy Land, including suffering an outbreak of disease in his fleet, he was excommunicated by Pope Gregory IX in 1227. The crusaders, led not by Frederick but by his representatives Richard Filangieri, Henry IV, Duke of Limburg, and Hermann of Salza, Grand Master of the Teutonic Knights, arrived in the east late in 1227, and while waiting for the emperor they set about refortifying Sidon, where they built the sea castle, and Montfort, which later became the headquarters of the Teutonic Knights. The Ayyubids of Damascus did not dare attack, as al-Mu'azzam had suddenly died not long before. Frederick finally arrived on the Sixth Crusade in September 1228, and claimed the regency of the kingdom in the name of his infant son.