Neither brother could raise the sum demanded by the Sultan and they were divided in their policies. While Demetrios, probably the more realistic of the two, had more or less given up hope of Christian aid from the west and thought it might be best to placate the Turks, Thomas retained hope that the Papacy might yet call for a crusade to restore the Byzantine Empire. Thomas's hopes were not ridiculous; the Fall of Constantinople had been received with as much horror in Western Europe as it had been in the few remaining Byzantine territories in the East. In September 1453, Pope Nicholas V issued the crusading bull "Etsi ecclesia Christi", which called on Christians throughout the west to take the cross and embark on a crusade to recover Constantinople. The response was enthusiastic; some of Europe's most powerful and influential rulers came forward to take the cross, including Philip the Good of Burgundy in February 1454 and Alfonso the Magnanimous of Aragon and Naples in November 1455. Alfonso promised to personally lead a host of 50,000 men and 400 ships against the Ottomans. At Frankfurt, Holy Roman Emperor Frederick III assembled a council of German princes and proposed that 40,000 men be sent to Hungary, where the Ottomans had suffered a crushing defeat at Belgrade in 1456. If the combined forces of Hungary, Aragon, Burgundy and the Holy Roman Empire had been unleashed to exploit the victory at Belgrade, Ottoman control of the Balkans would have been seriously threatened.