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.