'It is true,' Thalius whispered. 'It is true! The unravelling of a Prophecy three centuries old-the fate of the whole world to come-all of it boils down to this moment, a knife in the hand of a slave!' But Tarcho hushed him roughly.

Constantine whispered, his voice growing weaker, his face greyer, 'The world is a complicated place, Audax. The future is unknown. And yet we must make choices even so. What do you think such choices should be based on? Words burned into your back, or the judgement of a man like me?'

Audax felt detached from the world, as if he was going to faint. His arm, outstretched, was so stiff, his blood-soaked fingers so numb, that he could barely feel the knife any more, and he didn't know if he was keeping still or not.

And as the world turned to grey, he thought he saw the walls of the room break down, like a collapsed wall in the mine, revealing corridors leading off to misty destinations. Dimly he discerned that the Emperor was telling the truth, and so was Thalius, that momentous events affecting the lives of people for generations unborn depended on what he did in the next few heartbeats. Who was he to trust, then-who or what?

If Constantine had been Tarcho he would not have hesitated-Tarcho, the only person in his life save perhaps his dimly remembered mother who had ever been truly kind to him. And yet Constantine was enough like Tarcho that he found he trusted him. People were real, Audax thought. People and their characters and their judgements. That was all that mattered in the world. Words, prophecies, were nothing.

'Call your doctor,' he said.

Constantine's eyes did not move, but his expression softened. 'Philip. Come here. As slowly as you like, sir…'

Nobody dared move until the Greek doctor had taken the knife from Audax's hand, and then slowly extracted it from the Emperor's chest. Audax, released, fell back, his head ringing, and that strange sense of detachment evaporated, and the room closed up to become just a room once more.

After that there was an explosion of movement, a flashing of blades. Tarcho grabbed Thalius and Audax and pulled them out of the melee.

In the autumn of the year that Constantine died, Thalius arranged to meet Audax before the steps of the Temple of Claudius in Camulodunum.

He fretted how he would even find Audax. After all, twenty-three years had elapsed since that extraordinary audience with the Emperor. And besides, he dreaded leaving home. It was a market day, this bright autumn morning, and the town would be full of farmers and their wives and brats, their dogs and sheep and cattle, and the traders, prostitutes and petty thieves who preyed on them. Some days Camulodunum was more like a vast cattle pen than a town, he thought grumpily. At the exceptional age of seventy-five years old, Thalius found it increasingly difficult to get around, and on days like this he preferred simply to hole up in his townhouse.

But he had no choice, for this was the only day Audax could meet him. The boy had had to travel all the way from his posting in far Constantinople, using up most of his leave on the complicated journey across the western empire, and even then he was required to spend most of his time in Londinium, at the headquarters of the diocese of the four Britains. Well, if Audax was prepared to come so far, Thalius could pluck up the courage to step out of his own front door to greet him.

And after all, they were both here for old Tarcho.

The melee before the Temple was just as difficult as Thalius had feared. Vendors had set up stalls on the steps and even inside the colonnade itself. They filled the air with the stench of broiling meat, and sold clothes, bits of cheap jewellery, second-hand pottery, little miniatures of the divine Helena-endless bits of tat. There was hardly an item here that was new, hardly anything that hadn't been manufactured within a mile of this very spot.

Thalius could see a lot of barter going on, rather than cash sales-half a chicken for a pretty bit of jade, a scrip promising a day's labour on a thatched roof in return for a much-used, much-repaired amphora. Those who did have cash hoarded it, out of sight of the tax collectors, but Thalius was aware that the collectors and their spies were probably circulating through the marketplace even now. In an age when even the army was prepared to accept payments in kind, a black market didn't stay black for long. The market was a vastly unpleasant place to Thalius, making him feel like a mouse among a swarm of mice feeding off each other's garbage.

The people around him were unpleasant too. Almost all of them younger than him-well, he had been used to that for years-and they were coarse, uncivil, disrespectful to each other and worse to old duffers like Thalius. It was an age of selfishness, he thought, an age of ill manners. And it was all because of Constantine. Poor, foolish, long-dead Aurelia had been right, in her narrow way. The burden of excessive taxation, the huge and still growing gulf between rich and poor, had coarsened society at every level. But what other way was there?

Here, though, amid all the rubbish, was a table piled high with books. There were scrolls, heaps of wood slips, even some densely inscribed wax tablets. Thalius began to rummage; it was a relief simply to be handling books. But none was mint, and some didn't even look complete. And very many of them were utterly uninteresting (to him) treatises on various aspects of the Christian faith.

There was an awful lot of this stuff around. After Constantine's imposition of Christianity his bishops and theologians, drunk on sudden power and money, indulged in ferocious infighting over heresies and counter-heresies. People were addled by intriguing theological complexities, and nowadays read only the Bible and commentaries on it-if they read anything at all. And as the numbers of the illiterate grew, and as the literate retreated into mysticism, nobody thought any more, nobody questioned, nobody remembered that things had ever been different from the way they were now.

But Thalius quickly identified a Tacitus, a Pliny, a Cicero, relics of an age when people could still think, and argue, and write.

He looked into the gloom of the covered stall behind the table. A youth sat on a stool, chewing on some herb, watching a girl on the next stall with a lascivious leer. Thalius snapped his fingers. 'You!'

The boy's head swivelled to face him. 'You're talking to me?'

'Not by choice, but it does seem you're the purveyor of these books. What is their provenance?'

The boy scowled. 'What?'

Thalius sighed. 'Are you selling these books? Where did they come from?'

'House breakage,' said the boy. 'Prices as marked.' His Latin was coarse, simplified. He was perhaps sixteen, with a hard, surly expression. Thalius wasn't frightened of him, but he was somehow disturbed. Here was a boy who had grown up almost outside society as Thalius had known it, with no compulsion to obey the rules of civilised discourse. What a resource for the future of Britain and the empire!

Thalius ran a finger over the scrolls. They were probably the debris of a minor tragedy, no doubt once owned by some member of the curia, more or less like himself, who had failed to maintain his balance in the endless cliff-top walk that was civil life these days.

But there were some interesting titles. One was a story called The True History by a Syrian-Greek called Lucian. Thalius had read it as a boy, and had since sought out other tales of fantastic voyages to strange corners of the world, or beyond the earth altogether-not myths, which always seemed a little hollow to him, but notions of what might actually be possible. But he had learned to keep his interest in these speculations quiet. Literary snobs always claimed that such tales were for adolescent boys, that the authors were running out of plots, and characterisation was sacrificed for the sake of ideas. It did Thalius no good to protest that the ideas were the whole point. With regret he replaced the Lucian; he already owned a better copy, though not one he kept on display.