Simplicianus, who died in about the year 400, was the successor to St Ambrose as the Bishop of Milan. He had his first direct contact with Augustine before the latter’s baptism. 

Not many years later he was the person for whom Augustine prepared one of his very first written works after his episcopal consecration in Hippo. Simplicianus was probably first resident in Milan between the years 350 and 360 and instrumental in converting Victorious (Augustine: Confessions viii. 2). Later perhaps than this he became intimate with St Ambrose, whose father in the Christian faith he is called by Augustine. About 374, the year Ambrose was raised to the episcopate, and Simplicianus appears to have settled at Milan. He was held in deep reverence by St Ambrose, who was often consulted by him, and speaks of Ambrose’ continual study of Holy Scripture [St Augustine: Cofessions VIII, 2].

As reported in Book Eight of the Confessions, Augustine sought out Simplicianus for counsel. Augustine had by then experienced an intellectual conversion to Christianity, but was still struggling to make the necessary moral conversion that was soon to follow in the garden in Milan. Augustine was deeply impressed by the acceptance of Christ at the instigation of Simplicianus by the famous orator and philosopher in Rome, Marius Victorinus. Like Augustine, Simplicianus and Ambrose were both Christian Neo-Platonists.

Victorinus’ career mirrored Augustine’s; he was a successful professor of rhetoric and a prominent protagonist of Christianity before his conversion.Augustine desired for a similar conversion, but found himself restrained in taking this step by his sexual life and his preoccupation with daily matters. Instead of asking theoretical questions of Simplicianus, Augustine sought practical advice: “I wanted to consult with him about my troubles, so that he could propose a method fitted for someone in my disturbed condition, whereby I could learn to walk in your way.” [Confessions VIII, 1]  Augustine judged his meeting with Simplicianus as having been fruitful for himself.

When not long afterwards Simplicianus was Bishop of Milan and Augustine was a priest at Hippo, Simplicianus exhorted Augustine, in many letters, to exercise his genius and take time for exposition of the Scriptures. And so, in the beginning of his episcopate in Hippo, Augustine wrote in the year 396 his De diversis quaestionibus ad Simplicianum (“To Simplicianus, on various questions”). It took the form of two books, dealing with Scriptural interpretations of Pauline passages from the First Epistle to the Romans. Book Two focuses as well on sections of the Book of Kings. The work is significant for its exposition of aspects of Augustine’s theology of grace. He concludes with an illustration of his own conversion. This is a topic to which he would return in much more detail when he wrote his Confessions not long afterwards.

As well as appear in Augustine’s life, Simplicianus is featured in the myths surrounding the life of Augustine that were generated by members of the Order of St Augustine in the fourteenth century. A primary example of this myth-making authorship was Nicholas of Alessandria O.S.A., who referred to Simplicianus in his Sermo de beato Augustino (“Sermon about blessed Augustine”), which he delivered at the famed Augustinian studium generale in Paris in 1332. In a final section of Nicholas’ sermon, he asserts something that was factually impossible, i.e., that Augustine of Hippo not only was the founder of the Order of Saint Augustine, but also that in Italy after his baptism he had lived as a hermit himself.

Contrary to the testimony of Augustine himself, Nicholas stated that Augustine was baptised at the age of thirty, and went back to Africa at the age of thirty-three. This allowed Nicholas’ biography of Augustine a space of three years, where in actual fact there was only an interval of sixteen months between Augustine’s baptism in Milan at Easter 387 and his return to Africa in August 388. How did Nicholas make use of the “extra time” he had "made" in Augustine’s life? He wrote that, after his baptism, Augustine lived for a year in a hermitage of Ambrose and Simplicianus, and was their disciple. Untrue, but to Nicholas it was a convenient untruth!

Simplicianus’ appointment as Bishop of Milan in the year 397 was described by Paulinus in his Life of St. Ambrose (c. 46 AD). Simplicianus died in 400, and was succeeded as Bishop of Milan by Venerius.  

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