After a restless wandering among pagan philosophies in search of God, he found his first light in reading the Old Testament; the Gospel later strengthened him in the faith of Christ. Soon after receiving Baptism he was elected bishop, around 350, by unanimous will of the people and the clergy, and, although he had a wife and a daughter, he devoted himself entirely to the Church, intervening with unceasing activity in the struggle against Arianism, facing with strong spirit the not inconsiderable risks. In 356 he was indeed exiled by the Emperor Constantius to Phrygia; in exile H. had the opportunity to come into contact with Eastern theologians and to learn their Trinitarian and Christological doctrines, but even from Phrygia he was driven away, being judged, for his tenacious fidelity to orthodoxy and his intolerance of the machinations of heretics, a disturber of the East. He was sent to Gaul, from where he came to Milan, where he clashed with Auxentius, who enjoyed the Emperor’s protection.
Finally retiring to his diocese, he was able to devote himself to his beloved studies and to the commentary on the Psalms, until death overtook him on 13 November 367; in 1851 he was proclaimed a Doctor of the Church.
H. is one of the most notable figures of Western Christianity for having spread in it the theological doctrines of the East, and for having made explicit in the Western world the same role that Athanasius fulfilled in the East in the discipline against Arianism. Worthy of note is the way in which, before Augustine, he saw the relationship between ratio and fides, affirming the need for a balanced use of reason and faith, which, since both come from God, do not exclude each other but rather integrate one another. The De Trinitate, one of the most complete works to emerge from the struggle against Arianism, reveals the prudence and love with which H. ascended to the loftiest heights of Christology, now trusting in reason, now abandoning himself to faith. The twelve books of the De Trinitate are conducted with rigorous logical order and are at the same time warmed by the trembling prayer of the theologian, who seeks in God the light and the means to express the grave mysteries of the Trinity. H. is sometimes more pleasing than Augustine himself, because he shuns as much as possible the abstruse academic artifices of Augustinian metaphysics. It must however be regretted that the reader encounters difficulties in approaching H.’s works, which had to bend the Latin language to express subtle theological disquisitions and arduous Christological problems that had received profound development in the Greek language, far more suited than Latin to the most delicate nuances of thought. Nor had H. been able to find any help in the Gallic schools, which at that time were struggling between the weight of tradition and the search for new paths: the writer, aware of his difficulties, often asks God for help so that he may provide the means to express the new ideas (De Trin., I, 38; Tractatus super Psalmos, 13, 1).
The judgment that Jerome gives of H. as a writer can still be endorsed today: «Hilarius Gallicano co-thurmo additur et, cum Graeciae floribus adornetur, longis interdum periodis involvitur» (Ep. 58, 10).
The obscurity and contortion that are indeed H.’s gravest defects stand out even more in his poetry: the three surviving hymns, obscure, contorted, and irksome, have the sole merit of having opened the series of Christian hymnography with the intention of opposing the poetic activity of heretics.
His manifold activity includes the following works:
**Exegetical works:**
1) Commentary on Matthew (written before 355): H. follows the Trinitarian ideas of Tertullian and Novatian.
2) Tractatus super Psalmos (356): H. follows with moderation the allegorical method of Origen.
3) Tractatus in Iob: only two fragments survive, noted by Augustine.
4) Liber mysteriorum (365): H. demonstrates that in every event of the Old Testament the coming of Christ is announced.
**Dogmatic works:**
1) De Trinitate (356), in 12 books: H. demonstrates the consubstantiality of the Father, the Son, and the Holy Spirit against the assertions of heretics in general and of Arians and Sabellians in particular.
2) De synodis seu de fide orientalium (358), divided into two parts: in the first H. deals with the decrees of some Eastern councils, in the second he addresses the question of the terms “homousios” and “homoiusios,” adhering to the first term, accepted by the Council of Nicaea, but not entirely rejecting the second (for which H. was harshly criticized).
3) Apologetica ad reprehensores libri de synodis seu de fide (after 358): a defence against those who attacked H. for the previous work; only fragments survive.
**Historical and polemical works** (Fragmenta historica, Collectanea antiariana Parisina):
1) Opus historicum adversum Valentem et Ursacium (356–67), written at various times in his defence against the accusations levelled against him in various councils; contains the Liber primus ad Constantinum Augustum.
2) Liber secundus ad Constantinum Augustum (359): H. asks to be heard by the Emperor.
3) Liber contra Constantinum imperatorem (360): H. inveighs against the Emperor, who has denied him the requested audience.
4) Contra Auxentium (364), written after the Council of Milan against the Arian bishop; only fragments survive.
5) Libellus contra Dioscorum medicum ad Sallustium praefectum (360), of which nothing remains.
**Hymns:** only three authentic ones survive: one on the unity of the Father and the Son (metre: glyconic, lesser asclepiadean); a second on the redemption of man (metre: iambic senarii); a third on the Incarnation of Christ (metre: trochaic septenarii).
**Letters:** are lost; those reported under his name must be considered spurious.