Isaac, emperor of Constantinople, had been dethroned by his brother Alexius. Abandoned by all his friends, deprived of sight, and loaded with irons, this unhappy prince languished in a dungeon. The son of Isaac, named also Alexius, who shared the captivity of his father, having deceived the vigilance of his guards and broken his chains, had fled into the West, in the hope that the princes and kings would one day undertake his defence, and declare war against the usurper of the imperial throne. Philip of Swabia, who had married Irene, the daughter of Isaac,[76] received the young prince kindly; but he was not then in a position to undertake anything in his favour, being fully engaged in defending himself against the arms of Otho and the menaces of the Holy See. Young Alexius next in vain threw himself at the feet of the pope, to implore his assistance. Whether the pontiff saw in the son of Isaac only the brother-in-law of Philip of Swabia, then considered an enemy to the court of Rome, or whether all his attention was directed towards the East, he gave no ear to the complaints of Alexius, and seemed to dread countenancing a war against Greece. The fugitive prince had in vain solicited most of the Christian monarchs, when he was advised to address himself to the Crusaders, the noblest warriors of the West. The arrival of his ambassadors created a lively sensation at Venice; the knights and barons were impressed with generous pity by the account of his misfortunes; they had never defended a more glorious cause. To avenge injured innocence, to remedy a great calamity, stirred the spirit of Dandolo; and the proud republicans, whose head he was, feelingly deplored the fate of a fugitive emperor. They had not forgotten that the usurper preferred to an alliance with them one with the Genoese and Pisans; it appeared to them that the cause of Alexius was their own, and that their vessels ought to bear him back to the ports of Greece and Byzantium.