Early career.
Though Ambrose, the second son of the prefect (imperial viceroy) of Gaul, was born in the official residence at Augusta Treverorum (Trier), his father died soon afterward, and Ambrose was reared in Rome, in a palace frequented by the clergy, by his widowed mother and his elder sister Marcellina, a nun. Duly promoted to the governorship of Aemilia-Liguria in c. 370, he lived at Milan and was unexpectedly acclaimed as their bishop by the people of the city in 374.
Ambrose, a popular outsider, chosen as a compromise candidate to avoid a disputed election, changed from an unbaptized layman to a bishop in eight days. Coming from a well-connected but obscure senatorial family, Ambrose could be ignored as a provincial governor; as bishop of Milan he was able to dominate the cultural and political life of his age.