The Austrian noblemen rose up in open rebellion against Frederick III of Germany, who governed the duchy in the name of Ladislaus the Posthumus at the turn of 1451 and 1452. The leader of the rebellion, Ulrich Eizinger sought the assistance of the Estates of Ladislaus's two other realms, Bohemia and Hungary. The Diet of Hungary, which assembled in Pressburg/Pozsony in February 1452, sent a delegation to Vienna. On 5 March the Austrian and Hungarian Estates jointly requested Frederick III to renounce the guardianship of their young sovereign. Frederick, who had been crowned Holy Roman Emperor, initially refused to satisfy their demand. Hunyadi convoked a Diet to discuss the situation, but before the Diet made any decision the united troops of the Austrian and Bohemian Estates forced the Emperor to hand over the young monarch to Count Ulrich of Celje on 4 September. In the meantime, Hunyadi had met Jiskra in Körmöcbánya (present-day Kremnica, Slovakia) where they concluded a treaty on 24 August. According to the treaty, Jiskra retained Léva (present-day Levica, Slovakia) and his right to collect the "thirtieth"a custom dutyat Késmárk (present-day Kežmarok, Slovakia) and Ólubló (present-day Stará Ľubovňa, Slovakia). In September Hunyadi sent envoys to Constantinople and promised military assistance to the Byzantine Emperor Constantine XI. In exchange, he demanded two Byzantine forts on the Black Sea, Silivri and Misivri, but the Emperor refused.