BARCOS, MARTINO DE. - Jansenist theologian, b. at Bayonne in 1600, d. 22 Aug. 1678. Nephew of Jean du Vergier de Hauranne, the celebrated Abbot of S. Cyran, he studied at Louvain under Jansenius together with his cousin d'Anguibert. After the death of his cousin, he became secretary to his uncle and collaborated with him in the composition of the *Petrus Aurelius* (1631-46) and with the celebrated Arnauld d'Andilly—whose son he had been tutor—to that of *Frequent Communion*, the fatal origin of all his future controversies. Supported by the queen mother, on 9 May 1644 he succeeded his deceased uncle in the governance of the Abbey of S. Cyran, which he set about reforming; there, after a period of exile, he died. Along with other Jansenist authors and in the wake of Gallicanism, he sought to undermine the authority of the Roman Pontiff.
His principal works are: *De l’autorité de s. Pierre et de s. Paul qui réside dans le pape successeur de ces deux apôtres*, s.l. [1645], published anonymously, in which B. propounds his theory—set forth in other later publications—that the two apostles had equal right to the title of supreme pastors of the Church. The work was condemned by the Holy Office on 24 Jan. 1647, and on 29 Jan. the doctrine itself was specifically condemned (Denz.-U., 965); *La grandeur de l’église romaine établie sur l’autorité de s. Pierre et de s. Paul* (s.l. 1645); *Epistola ad Innocentium de suprema ecclesiae romanae amplitudine* (s.l. [1645]), both placed on the Index on 24 Jan. 1647; *Éclaircissements de quelques objections que l’on a formées contre la grandeur de l’église romaine* (s.l. 1646); *Quae sit s. Augustini et doctrinae ejus auctoritas in Ecclesia* (Paris 1650); *De la foi, de l’espérance et de la charité* (2 vols., Antwerp n.d., reprinted at Châlons 1691); *Exposition de la foi de l’église romaine touchant la grâce et la prédestination* (Mons 1696; placed on the Index 24 Apr. 1697).