On 1 May 1566, Suleiman I led an Ottoman invasion of Habsburg-controlled Hungary, the Ottoman forces of which was one of the most sizable armies he had led in his rule of 46 years. After reaching Belgrade and met with John II Sigismund Zápolya on 27 June, Suleiman I learned that a Croatian-Hungarian nobleman, Nikola IV Zrinski, Ban of Croatia, accomplished an attack on an Ottoman military camp at Siklós. Suleiman I held off his attack of Eger for the time being, and began to set off towards Nikola IV Zrinski's fortress at Szigetvár. From 2 August to 7 September, the Ottoman forces had laid siege to the fortress with a force, at the least, of 150,000 against Zrinski's 2,300 defenders. While the siege turned into a victory for the Ottomans, it came at the cost of: 25,000 Ottoman soldiers and Suleiman I, who before the final battle of Szigetvár, due to natural causes of old age and illness.