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 (15[1])kingdom (15[1])used the ouroboros and crusader imagery when founding the Order of the Dragon. After (-5[1])receiving other (-5[1])titles, that ruler of this (-5[1])kingdom (-5[1])organized the election of Pope Martin V at the Council (15[1])of Constance. A ruler of this kingdom hired the standing (*) “Black (10[1])Army” of (10[4])mercenaries (10[1])and amassed the (10[1])largest (10[1])library outside of Italy, which was later brought to (10[1])Istanbul (10[1])after his 1490 death. Matthias Corvinus (10[1])and (10[1])John Hunyadi ruled this (10[1])kingdom, which (10[1])fought the Ottomans at battles like Varna before being decisively (-5[1])defeated in 1526 at Mohács [moe-hatch]. For 10 points, name this kingdom founded by the Árpád (10[1])dynasty that became the (10[1])main eastern part of the Habsburg realm. (10[3])■END■