The man who best incarnated fourth-century Christianity in all its aspects, a Christianity which was by then well on the way to taking over the world, was indisputably St Ambrose, the great Bishop of Milan. Emperor Theodosius was to say, after a dramatic conflict in which both men had been opposed to each other: “Of all those whom I have known, Ambrose alone really deserves to be called a bishop.”

Ambrose was the living model and perfect expression of that Christian élite which, attached by all its fibres to the bases of the existing civilisation, but transforming them by virtue of a new intention, alone knew how to assume the responsibilities of the age and take an option on the future. He lived in an age of great uncertainty and led a Church that was just developing its structures and order.

Ambrose was to be Bishop of Milan for twenty-four years, until his death; bishop in the fullest sense of the word, fulfilling his function in a manner that allows him no equal. Certainly no man of his age possessed so many of the qualities needed to assume the difficult episcopal functions, made more difficult in his case by the fact that had to exercise them in the imperial capital, alongside rulers eager to encroach on his preserves. Everything about him, therefore, marks Ambrose as an eminently representative figure of early Christianity in a period of great transition in the years when the Roman Empire was about to collapse.