To support a ruler of this kingdom defending a siege, Calixtus III began the practice of the ringing of the Noon Bell. A ruler of this kingdom used the ouroboros and crusader imagery when founding the Order of the Dragon. After receiving other titles, that ruler of this (-5[1])kingdom organized the election of Pope Martin V at the Council of Constance. A ruler of this kingdom hired the standing (*) “Black (10[1])Army” of (10[1])mercenaries and amassed the largest library outside of Italy, which was later brought to Istanbul after his 1490 death. Matthias Corvinus (10[1])and (10[1])John Hunyadi ruled this kingdom, which (10[1])fought the Ottomans at battles like Varna before being decisively defeated in 1526 at Mohács [moe-hatch]. For 10 points, name this kingdom founded by the Árpád dynasty that became the main eastern part of the Habsburg realm. (10[1])■END■