The successful defence of Belgrade in July 1456 exemplified just such limited crusading. Mehmed II advanced up the Danube in the summer of 1456, laying siege to Belgrade in the first week of July. He hoped, once the city had fallen, to press on to Buda before the campaign season ended. Facing him at Belgrade, the modest garrison was minded to come to terms. However, unexpected reinforcements arrived, led by John of Capistrano, a seventy-year-old Observant Franciscan with a long history of enthusiasm for crusading and moral rearmament. His interest in the recovery of the Holy Land and the Turkish question stretched back to the 1440s, part of his order’s longstanding involvement in preaching against enemies of the church, including heretics and Jews. Well connected, John had visited the Burgundian court in March 1454 and attended the German imperial diet at Frankfurt in November. He began preaching the crusade. By the spring of 1455, John was in Hungary concocting with a probably sceptical Regent Hunyadi an absurd plan for a huge international crusade of 100,000 men. More constructively, John toured the region preaching and establishing his credentials as a religious reformer. Credibility among crusade preachers assumed great importance. A few years later Pius II acknowledged the damage from past deceit, corruption and idleness: ‘People think our sole object is to amass gold. No one believes what we say. Like insolvent tradesmen we are without credit’. Only ostentatious displays of simplicity and sincerity could anaesthetize such feelings. John exuded the right balance of personal holiness and practical direction.

John’s preaching in Hungary, begun in May 1455 but reaching a crescendo of intensity between February and June 1456, was carefully orchestrated. Reflecting both his age and careful organization, progress was measured: 375 miles in fourteen months, less than a mile a day. In February 1456, in a well-publicized ceremony at Buda, John took the cross from the papal legate, John of Carvajal. According to John, at least, his evangelism was enormously successful, especially with ‘the lesser folk’. Hunyadi’s strategy appeared to have two elements. He concentrated on enlisting a reluctant nobility while John and his fellow preachers provided the focus for raising the general popular military levy, based on the so-called militia portalis system in use for a couple of generations. This system of peasant military levy meant these nonnoble recruits possessed at least rudimentary arms and probably some basic training. John’s transparent sincerity mitigated any social or fiscal resentment a summons from the nobles may have aroused, his appeal deliberately transcending secular hierarchy. Little was left to chance. Local bishops lent their support. News of his preaching was carefully spread before his arrival. Sometimes, congregations were disappointed, one being kept waiting for over a week without John appearing. Recruits also came from outside Hungary, mainly Austria and Germany, including, apparently, hundreds of students from Vienna university, perhaps seeking a glamorously adventurous summer vacation away from the lecture halls. John’s efforts formed only the centrepiece of a campaign that led to a summer of cross-taking in parts of Hungary, attracting very positive reports. Observers may have been pleasantly struck by the focus on raising men rather than the more usual touting for money. John’s contribution may have been exaggerated in his own writing and the hagiographical accounts that soon clustered around the events of 1456. Nonetheless, he raised a significant army, perhaps some thousands strong, even if its cohesion suggests it was held together by more than the friar’s personality alone.

Despite apologists’ sentimental insistence on the wondrous and miraculous, John of Capistrano’s crusader army, while not necessarily the collection of inspired and devoted civilian innocents of propaganda and legend, played an important role in the defence of Belgrade. They supplied numbers and vital morale. The Hungarian garrison was too small to combat the Turks outside the walls of Belgrade and, without relief, was unlikely to have withstood Turkish bombardment indefinitely. Mehmed may also have relied on the longstanding reluctance of elements in the Hungarian nobility to fight if an accommodation were available. The arrival of John’s troops from 2 July onwards allowed for more aggressive tactics. They helped Hunyadi break the Turkish naval blockade around the city on 14 July. A week later, on the night of 21–2 July, they stood with the garrison in the breaches of the battered city walls to repulse the main Turkish assault. The following day, as Mehmed began to organize his retreat, they formed a major element in the counter-attack that swarmed over the Turkish forward positions, inflicting further heavy casualties and seizing large amounts of matériel. The success of John’s recruiting effort seems to have wrong-footed Mehmed, whose plans depended on a relatively rapid seizure of Belgrade if his further targets were to be met. The crusaders’ appearance in strength dashed hopes that his initial superiority of numbers and control of the rivers would force Belgrade’s surrender. That Ottoman forces were stretched is confirmed by their precipitate withdrawal once the desperate ploy of a night-time frontal assault failed.

The well-attested tensions between John’s crusaders and Hunyadi added lustre to the image of a providential force whose faith triumphed where military prowess and professionalism had failed. In fact, much of the antagonism between the two groups revolved around the disposition of booty and Hunyadi’s lack of control over the crusaders, a consequence of the decision earlier in the year to give John a measure of autonomous authority over his recruits. However, John showed his understanding of the proper relationship of his army to Hunyadi when, the day after the Turks’ departure, he summarily disbanded his troops when they tried to assert their independence by claiming sole credit for victory and, thus, ownership of its spoils. John and his crusaders’ reputation owed most to the search, then and since, for heroes who could be shown achieving temporal success through living up to the highest spiritual standards crusade rhetoric demanded. Undoubtedly, John’s spiritual charisma helped bond his army together and to the cause. His banners spoke both of crusading and the morally strict programme of his order. Revivalism had perennially fuelled crusade enthusiasm, especially in default of the secular discipline or coercion of enforceable lay hierarchies and secular lordship. But such effervescent popular crusading tended to evaporate quickly, John of Capistrano’s crusade proving no exception. His army disbanded and he himself died of the plague in October 1456. Thereafter garrisons and truces kept the Ottomans at bay and out of Hungary until the 1520s, not crusaders, indigenous or foreign.

The more conventional efforts of Calixtus III wholly failed to defend Hungary. His fleet only managed to set out in August 1456, meeting with modest success during a tour of duty that lasted until late 1457. Lemnos, Samothrace and Thasos were recovered in the Aegean; a Turkish fleet was defeated at Mytilene in the summer of 1457, and an uplifting but pointless raid was conducted down the Levantine coast to Egypt. Pope Calixtus milked these successes. The naval victories were commemorated by a medal, that at Belgrade by the institution in 1457 of general observance of the Feast of the Transfiguration on 6 August, the day news of the triumph had reached Rome a year before. It was also the date of the battle of Mytilene. Yet such gestures did little to deflect the consolidation of Ottoman power south of the Danube and in Greece. The flow of the Ottoman advance may have been stemmed, but there was no counter-attack. The overwhelming presence of Turkish dominion from Serbia to Cilicia remained unaltered, a fact that preyed heavily on Calixtus III’s successor, called by some ‘the last crusader’.