to reduce the power of the Tuscan cities. In 1186, he engineered the marriage of his son Henry to Constance of Sicily, heiress to the Kingdom of Sicily, over the objections of Pope Urban III. Pope Urban III died shortly after, and was succeeded by Pope Gregory VIII, who even as Papal Chancellor had pursued a more conciliatory line with the Emperor than previous popes and was more concerned with troubling reports from the Holy Land than with a power struggle with Barbarossa. Third Crusade Around 23 November 1187, Frederick received letters that had been sent to him from the rulers of the Crusader states in the Near East urging him to come to their aid. Around 1 December, Cardinal Henry of Marcy preached a crusade sermon before Frederick and a public assembly in Strasbourg. Frederick expressed support for the crusade but declined to take the cross on the grounds of his ongoing conflict with Archbishop Philip of Cologne. He did, however, urge King Philip II of France to take the cross through messengers and then in a personal meeting on 25 December on the border between Ivois and Mouzon. On 27 March 1188, at the Diet of Mainz, the archbishop of Cologne submitted to Frederick. Bishop of Würzburg, Godfrey of Spitzenberg, preached a crusade sermon and Frederick asked the assembly whether he should take the cross. At the universal acclaim of the assembly, he took the crusader's vow. His second son, the duke of Swabia, followed suit. The eldest, Henry VI, was to remain behind in Germany as regent. At Mainz Frederick proclaimed a "general expedition against the pagans". He set the period of preparation as 17 April 1188 to 8 April 1189 and scheduled the army to assemble at Regensburg on 23 April 1189. At Strasbourg, Frederick had imposed a small tax on the Jews of Germany to fund the crusade. He also put the Jews under his protection and forbade anyone to preach against the Jews. When mobs threatened the Jews of Mainz on the eve of the assembly in March, Frederick sent the imperial marshal Henry of Kalden to disperse them. Rabbi Moses then met with the emperor, which resulted in an imperial edict threatening maiming or death for anyone who maimed or killed a Jew. On 29 March, Frederick and the rabbi rode through the streets together. Frederick successfully prevented a repeat of the massacres