denomination in June. John Sigismund also adopted Calvinism and made Ferenc Dávid his court preacher. Wars and debates Ferdinand died on 25 July 1564, and his son Maximilian II succeeded him. The Transylvanian Diet declared war to reoccupy the counties that had been lost to the Habsburgs in 1562. John Sigismund's army seized Szatmár (now Satu Mare in Romania), Hadad and Nagybánya (now Baia Mare in Romania) before the end of 1562, but a counter-invasion by Lazarus von Schwendi reached the river Szamos in March 1565. The envoys of John Sigismund and Maximilian II concluded a treaty in Szatmár on 13 March 1565 in which John Sigismund renounced his title of king in return for the recognition of his hereditary rule in Transylvania John Sigismund was also to marry Maximilian II's sister, Joanna. However, the Ottomans forced John Sigismund to declare the treaty null and void on 21 April. John Sigismund and Hasan, Pasha of Temesvár, joined forces and recaptured Erdőd (now Ardud in Romania), Nagybánya and Szatmár. He intended to see the sultan in Istanbul to give an explanation for the Treaty of Szatmár, but Suleiman informed him that he would personally come to Hungary. Ferenc Dávid began to include Anti-Trinitarian ideas in his sermons, which infuriated the Calvinist bishop of Debrecen, Péter Melius Juhász. John Sigismund organized an open debate about the doctrine of Trinity, which was held in Gyulafehérvár in April 1566. After the debate John Sigismund granted funds to the Calvinist publishing house in Debrecen. He also sponsored the establishment of Protestant colleges in Kolozsvár, Marosvásárhely (present-day Târgu Mureș in Romania) and Nagyvárad. His letters to Petrus Ramus and other leading scholars of the Reformation show that he wanted to develop the royal college in Gyulafehérvár into an academy. An anthology of Italian poems, published in Venice in the 1560s, hailed John Sigismund as "patron of the Renaissance". Sultan Suleiman came to Zemun on the Danube in preparation for his campaign against Habsburg territories in the summer of 1566. John Sigismund hurried to the sultan's camp, accompanied by 400 Transylvanian lords. After John Sigismund and his principal advisors prostrated themselves before the sultan in his tent, Suleiman confirmed John Sigismund's position as hereditary ruler. According to the eyewitness Mustafa Selaniki, the sultan addressed John Sigismund as his "beloved son". John Sigismund invaded Upper Hungary on the sultan's order on 28 July. However, when Suleiman died during