MARTIN V. (Otto Colonna) (1417-1431) was elected at Con stance on St. Martin's Day, in a conclave composed of twenty three cardinals and thirty delegates from the five different "nations" of the council. Having become a cardinal under Inno cent VII., he had seceded from Gregory XII. in 1408, and together with the other cardinals at Pisa, had taken part in the election of Alexander V. and afterwards of John XXIII. At Constance, his role had been chiefly that of an arbiter; he was a good and gentle man, leading a simple life, free from intrigue. While refraining from making any pronouncement as to the validity of the decrees of the fourth and fifth sessions, which had seemed to proclaim the superiority of the council over the pope, Martin V. nevertheless soon revealed his personal feelings by having the constitution read in consistory which forbade any appeal from the judgment of the sovereign pontiff in matters of faith (May 1o, 1418).
Martin V. himself settled a great number of points, which had been raised at the council, and then passed a series of special concordats with Germany, France, Italy, Spain and England. Though this was not the thorough reform of which need was felt, the council itself gave the pope a satisfecit. When the council was dissolved Martin V. made it his task to regain Italy. After staying for long periods at Mantua and Florence, where the deposed pope, Baldassare Cossa (John XXIII.), came and made submission to him, Martin V. was enabled to enter Rome
(Sept. 3o, 1420. He set to work to repair the damage done by the Great Schism, to enter into negotiations, unfortunately unfruitful, with the Greek Church also with a view to a return to unity, to organize the struggle against heresy in Bohemia ; to interpose his pacific mediation between France and England, as well as between the parties which were rending France ; and, finally, to welcome Bernardino of Siena and Francesca Romana, foundress of the nursing sisterhood of the Oblate di Tor de' Specchi (1425).
Martin V., after an interval of five years, summoned a new council, which was almost immediately transferred from Pavia to Siena, in consequence of an epidemic (1423). It was quickly dissolved. Pending the reunion of the new council which had been summoned at Basel, Martin V. himself endeavoured to effect a reformation in certain points, but he died (Feb. 20, just as he had designated the young and brilliant Cardinal Giuliano Cesarini to preside in his place over the council of Basel.
See L. Pastor, Geschichte der Piipste (19ot), i. 205-279; J. Guiraud, L'Etat pontifical apres le Grand Schisme (1896) ; Miintz, Les Arts a la tour des pages pendant le xve et le xvie siecle (1878) ; N. Valois, La Crise religieuse du xve siecle; le pape et le concile (19o9), vol. i. p. i.—xxix., 1-93.