The resentful spirit of Urban, stimulated by the hostile conduct of the rebellious cardinals, prompted him to meditate a severe revenge. He instantly dispatched an ambassador to Lodovico, king of Hungary, with instructions to proffer to that monarch his assistance in punishing the queen of Naples, for the imputed murder of her husband Andrew, brother to the Hungarian sovereign, who it was alleged had, with her concurrence, been put to death by Luigi, prince of Taranto.[13] Lodovico, who had long thirsted for vengeance, eagerly accepted the offers of Urban, and gave orders to Carlo, son of Luigi di Durazzo, the descendant of Charles II. and heir apparent to the throne of Naples, to march with the Hungarian troops, which were then engaged in hostilities against the Venetians, and to co-operate with the pope in an attack upon the kingdom of Naples.[14] Carlo, after taking Arezzo, and making peace with the Florentines on the condition of their lending him forty thousand crowns of gold, repaired to Rome, where he held a conference with Urban. Thence he directed his march to Naples, of which city he easily made himself master. Joanna, after sustaining a short siege in the Castello Nuovo, was taken prisoner, and, according to the directions of the inexorable king of Hungary, smothered between two mattresses.[15] This vindictive deed being perpetrated, Urban repaired to Naples, and, according to the terms of an agreement which had been concluded before the departure of the prince of Hungary from Rome, he demanded, on behalf of his nephew, the possession of the principality of Capua, and of several other places in the kingdom of Naples. On Carlo’s refusing to accede to this demand, Urban, with characteristic impetuosity, had recourse to threats, to which the king answered by putting the pontiff for some days under an arrest. Urban, dissembling his indignation, requested, and obtained of the prince, permission to retire to Nocera for the benefit of his health. The first step which he took on his arrival at that place, was to strengthen its fortifications, and recruit its garrison. He then proceeded to the nomination of new cardinals, and threw seven members of the sacred college into prison, alleging, that at the instigation of Carlo, and of his rival Clement, they had formed a conspiracy against his life. Having cited the Neapolitan monarch to appear and answer to the charges which he had to prefer against him, he proceeded to his trial. Carlo treated the summons with contempt, and sent Count Alberico, grand constable of his kingdom, at the head of an army to lay siege to Nocera. Urban, escaping from that city, embarked with his prisoners on board some Genoese galleys, which had been prepared to aid his flight. Exasperated to the highest degree of cruelty, the fugitive pontiff vented his fury on the captive cardinals, five of whom he caused to be tied up in sacks, and thrown into the sea.[16]