‘In the short term, perhaps. But we are living with the long-term consequences of Hadrian’s decision, Tarcho. And what do we find? Secure beyond a frontier fixed in stone, the barbarians have organised, federated, found capable leaders, and now break through the Wall to crush us. But if Hadrian had taken the land of the Caledonians they would be Roman by now, and Britain would be secure, at least internally. Think of it - a whole island to serve as a garrison for western Europe. Couldn’t Gaul and Spain then have been defended when the Franks and the Goths came?’

‘Yes, well, if you want to know what I think,’ Maria said suddenly, ‘we all got into this mess because of the way Constantine barbarised the empire. That’s my view. That’s why Gaul is full of Franks and Spain is full of Goths and the south of Britain is full of Saxons. I know, I’ve been down there. They care nothing for our ways and they’re only out for themselves. And now, who is strong enough to throw them out? Nobody, that’s who.’

Tarcho grunted. ‘I see what you’re driving at about Hadrian, Nennius. But she’s right. If it’s decisions and their dire consequences you want to talk about it’s Constantine you have to consider. After all he did move his capital to Constantinople, taking all the money with it.’

‘Then there’s another possibility,’ Nennius said. ‘Suppose Constantine, instead of moving his capital to the east, had moved it west—to Gaul, even to Britain itself, where he was after all elevated. Imagine the empire run from Londinium or Eburacum! Why not? Britain was stable, relatively, and rich too: its corn and metals supplied the armies on the Rhine and the Danube for generations. That is why Britain has been the seat of one usurper after another, including Constantine himself. And with the British garrison behind them, and the focus of the emperors here rather than in the greasy fleshpots of the east, isn’t it possible the empire could have been saved?’

Londinium as the capital of the Roman empire! The thought was so breathtaking it silenced them for a moment - and Isolde knew it wasn’t such a terribly implausible idea. After all many of the usurpers of the last few decades before the final British Revolution had tried to set up a separatist empire of the western provinces.

‘But I don’t see what difference any of this talking makes,’ Maria said now. ‘Maybe things could have been different if somebody had done this instead of that - but so what? What’s done is done. The past may have been malleable for those who lived in it, Nennius, but to us it is surely fixed.’