surnamed ARELATENSIS, was born at the commencement of the fifth century, in Gallia Belgica, of a noble family, and distinguished himself in boyhood by the zeal and success with which he followed out the various branches of a liberal education. At an early age he became the disciple of Honoratus, first abbot of Lerins, by whom he was persuaded to abandon the world, and to devote himself to a monastic life. To this he attached himself so warmly, that when the bishopric of Arles became vacant in A. D. 429, by the death of his preceptor, he was with the utmost difficulty induced to yield to the wishes of the clergy and people, and to accept the episcopal chair. The circumstance that a monk of twentynine should have been chosen unanimously to till such an important station is in itself a strong proof of the reputation which he must have enjoyed as a man of learning, eloquence, and piety. His name, however, has acquired importance in ecclesiastical history chiefly from the controversy in which he became involved with Pope Leo the Great. A certain Chelidonius, bishop either of Vesoul or Besancon, had been deposed, in consequence of certain irregularities, by a council at which Hilarius presided, assisted by Eucherius of Lyons and Germanus of Auxerre. Chelidonius repaired to Rome for the purpose of lodging an appeal against this sentence, and thither he was followed by Hilarius, who expressed a wish to confer with the pontiff, but refused to acknowledge his jurisdiction in the case. Leo, incensed by what he considered as a direct attack upon his supremacy, forthwith reinstated Chelidonius, while Hilarius, entertaining apprehensions for his own personal freedom, was fain to quit the city by stealth, and make his way back to his diocese, on foot, crossing the Alps at the most inclement season of the year. He subsequently endeavoured, but in vain, to negotiate a reconciliation with Leo, who refused to listen to any ternis short of absolute submission, and eventually succeeded in depriving him of all the privileges which he enjoyed as metropolitan of Gaul. This proceeding was confirmed by the celebrated rescript of Valentinian III., issued in 445, in which, among other matters, it was ordained, Ut Episcopis Gallicanis omnibusque pro lege esset, quidquid apostolicae sedis auctoritas sanxisset: ita ut quisquis Episcoporum ad judicium Romani antistitis evocatus venire neglexisset per moderatorem ejusdem provinciae adesse cogeretur, a decree which, while it unequivocally established the authority of the bishop of Rome over the church beyond the Alps, at the same time, when taken in connection with the circumstances by which it was called forth, seems to prove that up to this period such authority had never been fully and formally recognised. The merits of this dispute have, as might be expected, become a party question among ecclesiastical historians, who characterise the conduct of the chief personages concerned in the most opposite terms, according to the views which they entertain with regard to the rights of the papal chair. Hilarius died in 449, about five years after the deposition of Chelidonius.