'No indeed,' Thalius said. 'Come, let's visit him.'

They crossed the temple floor, threaded their way down the steps through the crowded market stalls, and made their way along the city's principal street. Once an axis of the invaders' fort of Claudian times, it was rubbish-strewn, its gutters clogged with dirt.

And as they walked, they spoke of the aftermath of the night of Aurelia's attempted assassination of the Emperor, the night that had entwined their fates for ever.

Constantine himself survived. His Greek doctor said that though his wound was deep, the narrow blade had fortuitously missed any major organs. Aurelia herself, who had hidden her fanaticism from Thalius until the moment of the attack, was cut down immediately by the blades of the Emperor's guards, and that was the end of her. Tarcho shielded Thalius and Audax from the guards, but they had all been taken into custody as the search for complicity began. The worthy missive Thalius had haplessly carried might have been enough, in the fevered atmosphere of a paranoid court, to see him executed. Thalius always believed it was Tarcho himself who saved him, by arguing forcefully with his military accusers for Thalius's naivete and innocence-not to put too fine a point on it, his stupidity.

As for Audax, he could have been executed with no questions being asked at all-or at the minimum tortured, for under Roman law slave testimony was only valid if extracted under torture. But if Tarcho had saved Thalius it was Constantine himself who saved Audax. In those moments when they had been joined in an embrace of life and death, the Emperor had seen something he liked in the slave, and he had pledged to protect him. When the fuss had died down Thalius hastily granted the boy his freedom and gave him into the care of Tarcho, who he judged was likely to do a much better job of keeping the boy safe than Thalius himself ever could.

As for the other principal in the drama, Ulpius Cornelius had made noises about the betrayal of his trust, receded into the shadows of the court, and Thalius had never seen him again. And he never knew if Cornelius had been complicit in the attempted assassination-if Thalius was the only dupe.

Tarcho had made good the Emperor's promise that Audax would have the chance to try life as a soldier. At the age of sixteen he was enlisted into the frontier garrison at Banna. He immediately flourished under the healthy food, medical supervision and training regime of the army; by the time he was eighteen he had shed the last shadow of the pale-as-a-ghost slave boy Thalius had dug up from the mine.

But he had rapidly proved too effective to be wasted in the stasis of a frontier post. On a letter of recommendation from Banna's commander, Audax was transferred away to the field army units in Gaul. Thalius saw him only rarely after that.

Audax was too young to fight in Constantine's first serious engagement with Licinius, Emperor of the east. It was a partial victory for Constantine; Licinius ceded territory but survived. The showdown came ten years after Constantine's visit to Britain, and by now Audax was old enough to serve.

'It was magnificent, Thalius,' he said now. 'They say it was the largest war for a century-there were perhaps a hundred and fifty thousand men on each side, and it raged across Europe and Asia for a year before Constantine's final victory near Byzantium…'

Audax forbore from telling Thalius any war stories, and the older man was glad of it. The civil was had been another terrible internal grinding-up of resources that could surely have been better deployed against external enemies, like the Franks and the Alamanna, new barbarian federations on the Rhine border, and the Goths on the Danube, and the revived Persians in the east. Even while Constantine fought Licinius, Visigoths had taken the chance to cross the Danube, and Constantine found himself at war along a front three hundred miles long.

After Constantine's victory over Licinius he called for Audax to join his own personal bodyguard, the scholae palatinae. 'You saved my life once already,' he said in Brigantian, on greeting the boy. 'So I believe I can trust you to do it again!'

So it was that Audax followed Constantine on the next great adventure of his reign-the move to the east. Again Aurelia had been right, and decade-old rumours were proved true. The site Constantine chose was Byzantium, a minor Greek city in Asia Minor-the place where he had won his final victory over Licinius. The new city was inaugurated only two years after that victory, and after some frantic rebuilding was dedicated four years after that.

'The new capital must be a marvellous place.'

'Not really,' Audax said candidly. 'It was thrown up quickly. Some of the new buildings are pretty shoddy, and it has attracted a scruffy class of people, I can tell you. It does have a forum and a senate of its own, and a dole of free grain, just like Rome. But it isn't Rome yet!'

'Ah, but it will grow.' And, Thalius thought sadly, soon the empire's wealth would flow from the east, from trade routes to India and beyond, and nobody would care about the western provinces with their poverty and long, vulnerable land borders: it was just as Aurelia had feared. But he said none of this to Audax. 'It is the epicentre of empire, and will be for a thousand years. And it was founded in our lifetimes, Audax. Think of that!'

The young man's eyes shone. 'I do miss you, Thalius. You always did fill me with a sense of wonder.'

Thalius, moved, took his arm. 'Then we must write. That way perhaps my fancy will enrich your life as your strength and courage have always enriched mine.'

They reached, at last, a small church. One of several in Camulodunum, it was modest, a boxy building on a rectangular plan. But it was neatly built of stone reused from some expensive ruin, and a wooden cross rose up above its tiled roof.

'Towards the end of his life, this is where Tarcho came to worship,' Thalius said. 'In fact this church grew out of a soldiers' chapel-there was once a mithraeum here, I think.'

Audax seemed briefly unable to speak. Then he said gruffly, 'And he is buried here?'

'Inside the church. His grave isn't marked.'

'It's a fitting place for a soldier.'

'Yes. The time was right for him to go, perhaps. He was always an admirer of Constantine, you know. A "good lad", he would say. He enjoyed reports of the preparations for a campaign against Persia. The dream of Alexander revived again, Tarcho said! I think it pleased Tarcho, in a way, to die in the same year as such a man.' He prompted gently, 'But Tarcho gone, and Constantine too-what next, do you think, Audax?'

'Things may be a little difficult,' Audax said with grim understatement. 'The campaign against Persia was controversial even in the Emperor's court. The east has always defeated the Romans if they push too far. And then there is the succession. Constantine's three sons have spent their youth fighting like puppies in a sack. I fear blood will be spilled before one of them emerges as top dog.'

Thalius sighed. 'And more strength bled from the body of the empire, while our enemies watch and wait. Audax, you must be careful.'

'I will be,' Audax said. 'I'm thinking of a change of posting, away from the court.'

'Then you're wise. You know, sometimes I am glad I am no longer young-sometimes it seems a comfort I won't see much more of the drama. But perhaps every old man thinks the world is decaying as fast as his body.'

'You mustn't think like that.'

'One must be realistic,' Thalius admonished him. 'But, Audax…' He asked cautiously, 'What of the Prophecy?'

Audax's face hardened. 'I suppose I have to thank it for saving my life. I'd have surely died in that hole in the ground if you hadn't come to find me, and it. But when I joined the army I had the tattoo burned off my back.'