bringing her son up "shamefully", allowing him to keep bad company and drink. John Sigismund's tutors were actually humanist scholars: the Hungarian Mihály Csáky and the Polish Wojciech Nowopołski. Nowopołski aroused John Sigismund's interest in theological debates. Ferdinand's rule remained fragile in the eastern territories of the Kingdom of Hungary because he did not send enough mercenaries to defend them. Suspecting that Martinuzzi was conspiring with the Ottomans, Castaldo had Martinuzzi murdered in late 1551. The Ottomans occupied the lowlands of Banat in the summer of 1552. In March 1553 Suleiman urged Isabella to return to Hungary. Péter Petrovics rose against Ferdinand, and an assembly of the Székely people declared their loyalty to John Sigismund. However, both uprisings were crushed before the end of September. Deciding in April 1554 that Hungary should be restored to John Sigismund, Suleiman allowed Péter Petrovics to take control of two fortresses in Banat. Henry II of France, engaged in war against the Habsburgs, also urged Isabella to return to Hungary, promising one of his daughters in marriage to John Sigismund. Suleiman sent messages to the Transylvanian lords in 1555, demanding they obey John Sigismund without resistance. Before the end of the year, the representatives of the Three Nations petitioned Ferdinand either to send reinforcements or to absolve them from their oath of fealty. Petrovics stormed into Transylvania in early 1556. The Diet swore an oath of fealty to John Sigismund on 12March 1556, referring to him as "the son of King John". The envoys of the Diet departed for Poland on 1June to persuade Isabella and her son to return. Two weeks later, Ferdinand informed Suleiman that he was ready to withdraw his troops from John Sigismund's former realm. Return The representatives of the Three Nations received Isabella and John Sigismund with much pomp and ceremony in Kolozsvár (now Cluj-Napoca in Romania) on 22October 1556. The Diet confirmed her right to administer state affairs in the name of her son, who was still a minor. In the following months several counties outside Transylvania (including Abaúj, Bihar, and Gömör) also acknowledged John Sigismund's rule. Isabella adopted a tolerant religious policy, enabling the spread of Calvinism, especially in Partium and Kolozsvár. In 1559 she started new negotiations with Ferdinand, proposing to renounce her son's title of king if Ferdinand would agree to marry one of his daughters to John Sigismund and to confirm John Sigismund's rule