'Carausias was no emperor but a usurper,' Thalius felt compelled to remind him. 'The purpose of the Invasion was to remove him. And of course taxes are higher now. Things have changed since the days of Hadrian, you know.'

Volisios looked confused. 'Who?'

'An emperor from ancient history,' Tarcho said. 'From a hundred years ago!'

'More like two hundred,' Thalius corrected him mildly. He pointed. 'You'll have to take those crosses down. The Emperor has banned crucifixion.'

'He has? Why?'

Tarcho said heavily, 'Why do you think? Because the Christ was executed on a cross.'

Volisios raised barely visible eyebrows at Thalius. 'Everybody is a theologian now, isn't that true?'

'No doubt,' Thalius said, 'those in your charge will be glad to hear the news.'

'Perhaps I won't tell them until I have to,' Volisios said, and he winked. 'Keep the bastards guessing-eh?'

Thalius looked again at the ugly crosses, and thought how strange it was that his own quest to do service to the man who had once died on such a cross had, in such a complicated fashion, brought him to this dismal place.

Volisios glanced up at the sky, where heavy clouds were clustering. 'Now, gentlemen, I think we'd better go underground. Believe me you don't want to be down there when it rains…Come, come this way. Watch your step, mind.'

He led them across broken ground to the mouth of a tunnel which gaped, black.

Thalius descended into the dark, climbing down ladders and staircases roughly cut into bare rock. He was over fifty years old and he felt stiff, awkward; he was unused to physical exertion. Again he was grateful for the presence of Tarcho, who went on below him.

'You'd think they would have some better way of getting important people down here,' Tarcho said. 'A nice wide staircase perhaps. Or a bucket on a rope!'

Volisios called up, 'It's rare anybody comes down if they don't have to.'

Tarcho said, 'If I was younger I'd sling you over my shoulder, Thalius.'

'I'll manage, Tarcho. Just be there to catch me if I fall.'

'I'll throw down the overseer so you'll have a soft landing!'

At last they reached the base of the chain of staircases. As Thalius and Tarcho caught their breaths, Volisios summoned a worker and whispered to him. The man ran off into the dark.

Thalius found himself standing on the rough-cut floor of a cave dug into the ground by the hands of men. There was a sound of running water, a stink of damp, and an unrelenting grind of wood on metal. The only light came from smoky oil lamps fixed to the walls. The place was hot, the smell of smoke strong; he had heard that the miners set fires to break up the rocks.

More shabby workers toiled here. Some of them hauled wooden carts laden with rock fragments; others watched the rest, holding whips and clubs, but the foremen were as grimy as those they controlled. Thalius saw passageways cut into the rock, leading off into a greater darkness. The passages were narrow, some not even tall enough for a man to stand upright, yet workers laboured there too.

That grinding, mechanical noise sharpened. Thalius peered up. In the shadows above his head vast wheels turned.

Volisios spoke with some pride of his family business. 'You can tell we've lots of water to play with here. We're served by two reservoirs. Up on the surface we use it for "hushing", washing off dirt and soil from ore outcrops, and down here to rinse away the bits of broken rock. Of course the deep galleries tend to flood, but we actually use running water to pump them out. See the waterwheels over your head? Their power hauls water from the sump up to the surface.'

Thalius was fascinated by the wheels in the air. He had always been intrigued by technology. 'Once I saw a water-organ playing in an amphitheatre in Gaul. Most remarkable thing I ever saw. Now I feel I'm trapped inside an even bigger machine.'

Tarcho pointed at the galleries. 'Those look awfully tight to me.'

Volisios eyed the old soldier's bulk with a touch of malice. 'Oh, if you were sent to work under me I'd soon thin you down. You find gold in veins in the quartz, and we make the passages no wider than the veins themselves. It's all to do with economy, you see.' He talked about other details of mining processes, in which the extracted ore was crushed and then panned in rocking wooden cradles, leaving tiny particles of gold to be captured by filters made of sheep's wool.

'I hear that in Germany,' Thalius cut in, 'they dig shafts in the ground to bring air to the tunnels. Not here?'

Volisios shrugged. 'It would cost too much.'

'But your miners must die in these holes in the ground.'

'They die anyway,' Volisios said, businesslike. 'You have to balance the cost of cutting the shafts against the cost of the labour.'

Tarcho said, 'Slaves aren't as cheap as they once were.'

'That's true. But convicts are always plentiful,' Volisios said. 'Always plenty more evaders for the tax inspectors to find and shove away down here.'

Thalius turned away. 'I can see why children are so useful to you in those rat runs-even if their little fingers have trouble picking apart the quartz, eh?'

Volisios faced him, cunning and caution in his eyes. 'You're judging me, aren't you? I'm only trying to make a living. This is a place of business, not an orphanage.'

'Perhaps you should bring me the boy now.'

Volisios glanced over his shoulder, and Thalius saw that the man the overseer had summoned earlier was standing in the shadows some way away, waiting. A smaller figure stood beside him, his thin arm held in the man's grip. Volisios snapped his fingers, and the man approached, pulling the boy with him. The boy didn't resist, but his limbs were loose, his head turned away; he was sullen, passive. 'This is the one you're looking for,' Volisios said. 'As far as we can tell, anyhow.'

Thalius felt his heart hammer.

The boy was brought into a pool of lamplight before him. Dressed in a rag, the boy was perhaps twelve, but he was so malnourished and skinny it was hard to tell. His joints were as lumpy as bags of walnuts, and his ribs under his ragged clothing were prominent enough to count. He was filthy, his face streaked with black. But despite that his oval face had a certain beauty, and the strawberry-blond colour of his hair showed through matted dirt.

Tarcho asked Volisios, 'What's his name?'

'Audax,' said the overseer bluntly. A common slave's name. 'He won't know anything about his family,' Volisios warned. 'He'd have been taken from his mother as soon as he was weaned.'

'If only I could see his face more clearly,' Thalius said. He bent to the boy and cupped his chin, meaning to lift his head. But Audax flinched, and Thalius realised that some of the marks around his mouth were bruises, not dirt. Thalius stepped back, uncertain how to proceed.

If Thalius was right about this boy's lineage, he came from a branch of his own family that had been cast into slavery for nearly two centuries.

When he had become interested in the ancestral legend of a lost Prophecy, he had traced the family history back to a bifurcation in the reign of Hadrian, when a brother of his own grandmother many-times-removed, Lepidina, had been sold with his mother (and Lepidina's), a woman called Severa, into slavery. Thalius knew he was fortunate that Lepidina had been spared that fate or he too would have been born a slave-if he had been born at all. Then Thalius had worked forward once more, tracing the fate of slaves and the children of slaves. Romans always kept good records, and even the tallying of slave transactions was surprisingly complete-but then, once the empire's expansion had been halted under Hadrian and the supply of new captives from conquered territories had dried up, slaves had become a commodity worth recording. At last he had followed the thread of lineage here, to this boy, Audax-who, if he was correct, was the very last of the line from that brother of Lepidina's.