“Next, every day a few of the rough ingots are held back from the cupellation hearth. It’s surprising how many, though I guess the number has crept up gradually over many years. This has the effect that the silver yield per ingot appears less than it really ought to be. I gather the declining yield was explained to Rome during Nero’s time as geological variations in the ore being mined. Things were notoriously slack then, so in case Vespasian has anybody looking at the figures it’s customary nowadays to slip in extra ingots some weeks, and claim the mineralogist has discovered a better seam.”

“Delicate touch!”

“Oh yes, we’re dealing with experts here. Will you be able to remember all this hogwash?”

“Have to try. Falco, trust me. Go on.”

“Right. Now, regarding the ingots of pure silver which are produced at the cupellation hearth. Some get lost. This is natural wastage.” Rufrius Vitalis scoffed admiringly again. “Then, when the lead bars that have had their silver extracted go back for a second smelt—”

“What’s that for?”

“To remove any other impurities before carting them out for sale—Mars Ultor, Vitalis, don’t let’s knot ourselves up in technicalities, this is complex enough as it is! Hilaris will know what the procedures are—” He shushed me to calm me down; I was sweating with the effort of ensuring I told him everything. Frowning, I pressed on. “After the second smelt more ingots disappear—though since their value is by then so much reduced, this last wrinkle in the system is considered to lack finesse! Apparently it’s permitted to the overseers, as a privilege that keeps them sweet.”

I fell silent. I was so unused to talking that presenting these details in an ordered form had tired me out. I could see Vitalis watching me closely, though after his first attempt he made no more suggestions for restoring me to civilization prematurely. My choice of comrade had been an intelligent one; I could see he understood the implications of what I had said.

“How do they get away with it, Falco?”

“It’s a completely enclosed community; no outsiders are allowed.”

“But they have a civilian settlement—”

“Where every baker, barber and blacksmith comes under licence, specifically to supply the mines! They’re all human; pretty well on arrival they are all suborned.”

“So what do those young dreamers at the fort think they’re playing at?”

There was a small fortress overlooking the settlement, an outpost of the Second Augusta which was supposed to supervise the mines. I smiled at Vitalis for his assumption that immediately after he himself retired, all military discipline went to the dogs.

“That’s the centurion in you talking! No one can blame them. All operations are subject to inspection, of course—”

“Both officers and men should be regularly changed—”