After these events, which occurred early in 1227, preparations for the crusade were pressed on, and the emperor sailed from Brindisi on the 8th of September. A pestilence, however, which attacked his forces compelled him to land in Italy three days later, and on the 29th of the same month he was excommunicated by the new pope, Gregory IX. The greater part of the succeeding year was spent by pope and emperor in a violent quarrel. Alarmed at the increase in his opponent's power, Gregory denounced him in a public letter, to which Frederick replied in a clever document addressed to the princes of Europe. The reading of this manifesto, drawing attention to the absolute power claimed by the popes, was received in Rome with such evidences of approval that Gregory was compelled to fly to Viterbo. Having lost his wife Isabella on the 8th of May 1228, Frederick again set sail for Palestine, where he met with considerable success, the result of diplomatic rather than of military skill. By a treaty made in February 1229 he secured possession of Jerusalem, Bethlehem, Nazareth and the surrounding neighbourhood. Entering Jerusalem, he crowned himself king of that city on the 18th of March 1229. These successes had been won in spite of the hostility of Gregory, which deprived Frederick of the assistance of many members of the military orders and of the clergy of Palestine. But although the emperor's possessions on the Italian mainland had been attacked in his absence by the papal troops and their allies, Gregory's efforts had failed to arouse serious opposition in Germany and Sicily; so that when Frederick returned unexpectedly to Italy in June 1229 he had no difficulty in driving back his enemies, and compelling the pope to sue for peace. The result was the treaty of San Germano, arranged in July 1230, by which the emperor, loosed from the ban, promised to respect the papal territory, and to allow freedom of election and other privileges to the Sicilian clergy. Frederick was next engaged in completing the pacification of Sicily. In 1231 a series of laws were published at Melfi which destroyed the ascendancy of the feudal nobles. Royal officials were appointed for administrative purposes, large estates were recovered for the crown, and fortresses were destroyed, while the church was placed under the royal jurisdiction and all gifts to it were prohibited. At the same time certain privileges of self-government were granted to the towns, representatives from which were summoned to sit in the diet. In short, by means of a centralized system of government, the king established an almost absolute monarchical power.