As Constantine’s campaign on foreign fields descended towards defeat, another turning point was reached. This time it wasn’t the officer corps or the ruling elite in the cities who rose up but the comparatively poor and lowly. What was the point of being taxed white by a centre which was better at producing usurpers than keeping out the barbarians? The revolt, once it broke out, spread like wildfire. The tax collectors were expelled from their offices and plush townhouses, and then the Christian poor turned on the still-pagan rich. The diocesan government collapsed. The middle-ranking officials in the towns and the four provincial governments decided to join the rebels, and legitimised and organised the revolt.

This ‘British Revolution’ was less than ten years old, and Isolde thought she detected pride about it in the calm voice of this church-man. Not that things were perfect. The four provincial governments had started to develop independent armies, mostly made up of Germanic mercenaries. But civilisation had been saved until the day came, as it must, when Britain was reunited once more with the centre of the Roman world of which it had always been part.

‘And it was a blow for freedom,’ Nennius said, enthused, eager for revolution in a way, Isolde thought a little sourly, only a comfortably plump old man far removed from the action could be. ‘Isn’t that a deep tradition in Britain? Why, you could say it informs the work of Pelagius himself.’

‘Ah, but never let Augustine hear you say that ...’

Isolde had met Pelagius herself once, as a little girl. About ten years older than her father, born in Britain, he was not a cleric, but he had developed forceful views about the direction of the Roman church, which he saw as corrupted, immoral and slothful. And he took great exception to the teachings of Augustine, a bishop from Africa, who argued that human beings were born fundamentally flawed, and that human actions depended on the will of God. Pelagius insisted that humans were essentially good, and were responsible for their own moral advancement.

‘But a church of free men and women cannot be controlled by the centre, and so it won’t do for an imperial cult,’ Nennius said gloomily. ‘Perhaps in future the Roman church will deal with all Pelagians as it has with Pelagius himself ...Think of it, Ambrosius! Excommunicated for proclaiming that mankind enjoys free will! What is the world coming to? Where is our church going?’

‘The question is, where are you going, my friend?’ Ambrosius asked with gentle humour, pouring more beer. ‘Are you still determined to find your cousin on the Wall? It won’t be an easy journey.’