Soon after this treaty, John Sigismond died, before his marriage with the emperor's niece, and Transylvania was again united to Hungary and came under the sway of Maximilian. This event formed quite an accession to the power of the Austrian monarch, as he now held all of Hungary save the southern and central portion where the Turks had garrisoned the fortresses. The pope, the King of Spain, and the Venetians, now sent united ambassadors to the emperor urging him to summon the armies of the empire and drive the Turks entirely out of Hungary. Cardinal Commendon assured the emperor, in the name of the holy father of the Church, that it was no sin to violate any compact with the infidel. Maximilian nobly replied, "The faith of treaties ought to be considered as inviolable, and a Christian can never be justified in breaking an oath." Maximilian never enjoyed vigorous health, and being anxious to secure the tranquillity of his extended realms after his death, he had his eldest son, Rhodolph, in a diet at Presburg, crowned King of Hungary. Rhodolph at once entered upon the government of his realm as viceroy during the life of his father. Thus he would have all the reins of government in his hands, and, at the death of the emperor, there would be no apparent change. It will be remembered that Ferdinand had, by violence and treachery, wrested from the Bohemians the privilege of electing their sovereign, and had thus converted Bohemia into an hereditary monarchy. Maximilian, with characteristic prudence, wished to maintain the hereditary right thus established, while at the same time he wished to avoid wounding the prejudices of those who had surrendered the right of suffrage only to fraud and the sword. He accordingly convoked a diet at Prague. The nobles were assembled in large numbers, and the occasion was invested with unusual solemnity. The emperor himself introduced to them his son, and recommended him to them as their future sovereign. The nobles were much gratified by so unexpected a concession, and with enthusiasm accepted their new king. The emperor had thus wisely secured for his son the crowns of Hungary and Bohemia.