Mehmed, the Ottoman governor of Belgrade, made a raid around Pest in March 1541. Ferdinand's commander, Wilhelm von Roggendorf, laid siege to Buda in May. Ferdinand's envoy, Niklas zu Salm, offered the region of Pressburg and Nagyszombat (now Bratislava and Trnava in Slovakia) to John Sigismund in return for Buda, but Martinuzzi refused. Martinuzzi personally participated in the defense of Buda Castle when the besiegers made a sudden assault on 11 June. Two days later, he ordered the persecution of a burgher who entered into secret negotiations with the besiegers about the surrender of the castle.