In July 1551, at Martinuzzi’s instigation, Isabella ceded Transylvania and the part of Hungary that remained in her hands to Ferdinand, in exchange for the towns of Ratibor and Oppeln in Silesia, and the Austrian troops, under the command of the Spaniard Castaldo, took possession of these territories.[279] When Solyman heard this news, he summoned Malvezzi before him, who pledged his life that there was no ground for this report; but, as he could not give satisfactory explanations, and fell back on the insufficiency of his instructions, he was thrown into prison in the Black Tower of the Castle of Anatolia on the Bosphorus,[280] the Sultan excusing this violation of international law by the argument that an ambassador was a hostage for the good faith of his master, and should suffer for any breach of it. From this incident it appears that the post of ambassador at the Porte was by no means unattended with danger. Ferdinand rewarded Martinuzzi by procuring for him a Cardinal’s hat, and appointing him Archbishop of Gran. Not content with these dignities, that wily politician made overtures to the Turks, with the object of gaining the sovereignty of Transylvania and Hungary for himself; but he was assassinated by Castaldo’s officers acting under Ferdinand’s orders, or, at any rate, with his connivance, at Alvincz, December 18, 1551. In 1552 the Turks recommenced their attacks on Hungary, which were attended with almost uniform success. In February they gained a victory at Szegedin; in April, Wessprim was taken by Ali, the Pasha of Buda; and in July Temeswar fell. Its capture was followed by the loss of the rest of the Banat. On August 11, Ali Pasha defeated an army of Ferdinand’s at Fülek, to the north of Buda, Sforzia Pallavicini was taken prisoner, and Sbardellatus Dudich, the Bishop of Waitzen, whom Busbecq calls by mistake the Bishop of Fünfkirchen, was killed.[281] Erlau, however, was besieged by Ali unsuccessfully. In April 1552, Ferdinand wrote to Roostem, the Grand Vizier, asking for Malvezzi’s release, and for a safe conduct for two more envoys. In consequence, Malvezzi was removed to the Seven Towers, and his allowance was increased; but he was still kept in close confinement.