After days on the road they were all hot, dirty, hungry, and the stench of the city lingered even here. There was no bath house, but the house had underfloor heating and hot water, and after an hour of pampering herself with her scents and creams Isolde felt almost human. She joined her host and his guests in a large, well-appointed triclinium.

The meal they were served relied heavily on meat, mostly mutton and pork, but there were olive oils and dates and a rather good fish oil, imports from the continent which, the bishop said, were a luxury these days. No wine, though, and Ambrosius apologised for serving them watery British beer, but it was strong enough to warm Isolde’s blood.

Her father, as usual, seemed to have forgotten she was here, and made no effort to include her in the conversation, and nor did Damon. But the bishop was gracious to her, and his servant, another young monk, was attentive to her needs. In the light of the low fire, as the aches of the journey were soothed away, Isolde was content to let the talk wash over her.

Ambrosius and Nennius were churchmen of a similar age, both in their late fifties, one from the heart of the empire, the other from its now-amputated limb, and they had lived through tumultuous times. And, like all men of their age, Isolde thought fondly, they believed the world was in decline, from a Golden Age a few decades before. Born a generation after Constantine, now known as ‘the Great’, they spoke reverently of the first Christian emperor, whose reign had been an interval of comparative peace.

But all over the known world the weather was bad. Even within the empire the great crops of wheat and millet which fed the large urban populations began to fail. Among the barbarians, as famine descended, pulses of refugees washed out of the heart of Asia, driving others before them, to press ever more relentlessly on the borders of the empire.

Constantine himself had stabilised the border by allowing barbarian peoples to establish new homelands inside the empire’s borders - vast numbers of them, for instance no less than three hundred thousand Sarmatians. This policy of ‘federation’ brought peace for a while, but there was much muttering about whether the empire could absorb such huge influxes.

There was trouble with the barbarians in Britain too. When Ambrosius was a boy of five, there was a ‘Barbarian Conspiracy’, a major invasion from several directions at once: by the Picts across the Wall, the Scots and Irish and Saxons from across the Ocean. For a whole year order was lost. Ambrosius and his family, he said, huddled inside the town walls as the children told each other blood-curdling tales of the baby-eating foreign savages who roamed the countryside.