Ambrose’s reputation after his death was unchallenged. For Augustine, he was the model bishop; at Augustine’s instigation a biography was written in 412 by Paulinus, deacon of Milan. To Augustine’s opponent, Pelagius, Ambrose was “the flower of Latin eloquence.” Of his sermons, the Expositio evangelii secundum Lucam (390; “Exposition of the Gospel According to Luke”) was widely circulated.

Yet, Ambrose is a Janus-like figure. He imposed his will on emperors, but he never considered himself as a precursor of a polity in which the church dominated the state, for he acted from a traditional fear that Christianity might yet be eclipsed by a pagan nobility and Catholicism uprooted in Milan by Arian courtiers. His attitude to the learning he used was similarly old-fashioned. Pagans and heretics, he said, “dyed their impieties in the vats of philosophy,” yet his sermons betray the pagan mysticism of Plotinus in its most unmuted tints. In a near-contemporary mosaic in the chapel of San Satiro in the church of San Ambrogio, Milan, Ambrose appears as he wished to be seen: a simple Christian bishop clasping the book of Gospels. Yet the manner in which he set about his duties as a bishop ensured that, to use his own image, the Catholic Church would rise “like a growing moon” above the ruins of the Roman Empire.