Following the conclusion of the western schism in favour of Rome at the Council of Constance (1415–1417), the new Pope Martin V returned to the Papal States after a three years-long journey that touched many Italian cities and restored Italy as the sole centre of Western Christianity. During the course of this voyage, the Medici Bank was made the official credit institution of the Papacy and several significant ties were established between the Church and the new political dynasties of the peninsula. The Popes' status as elective monarchs turned the conclaves and consistories of the Renaissance into political battles between the courts of Italy for primacy in the peninsula and access to the immense resources of the Catholic Church. In 1439, Pope Eugenius IV and the Byzantine Emperor John VIII Palaiologos signed a reconciliation agreement between the Catholic Church and the Orthodox Church at the Council of Florence hosted by Cosimo "the old" de Medici. In 1453, Italian forces under Giovanni Giustiniani were sent by Pope Nicholas V to defend the Walls of Constantinople but the decisive battle was lost to the more advanced Turkish army equipped with cannons, and Byzantium fell to Sultan Mehmed II.