 Aided by the Observant Franciscan preacher John Capistran, he gathered an army of about 40,000 men, effected a union with the troops of John Hunyadi, and on 22 July 1456 the siege of Belgrade, the key of the Danube, was raised by a victory that inaugurated the century-long resistance of Hungary to the Ottomans.In 1457, Carvajal baptized King Thomas of Bosnia into the Roman Catholic Church.Calixtus III died on 6 August 1458, but Cardinal Carvajal was not in Rome, and therefore did not participate in the Conclave that elected Cardinal Aeneas Silvius Piccolomini as Pope Pius II.