Talking to a frumentarius, even on this remote mountainside, Valens thought that it best not to be drawn into such potentially treasonous speculation. ‘When I was a boy, the slave of a neighbour on the Esquiline had these strange marks on his skin: circles, like those made by a cupping glass. My nurse said they were caused by a daemon.’

‘Dangerous things, daemons.’

‘She always said lots of them lurked in the baths.’

‘Maybe they like the dark and the steam.’

‘She said they smelt bad.’

‘That would account for them making their homes in the baths.’

‘You have never seen one?’

‘No, but that does not mean they do not exist.’ Aulus frowned with thought. It accentuated the sunken cheeks of his tired, pouched face. ‘If I meet one, I will try shouting, like Clemens said. If that does not work, I will see how it gets on with a dagger in its guts.’

Valens sat in silence, rather admiring this practicality.

‘Where on the Esquiline was your parents’ place?’ Aulus asked.

‘The Carinae.’

‘Nice district,’ Aulus said.

‘We better go and hunt for our daemon.’

The entrance to the caves was as tall as a man, and as wide as a farm gate. The floor sloped upwards, which would keep out the rain and the snow in winter. A short passage opened into a chamber the size of the atrium of a moderately well-to-do house.

Scattered around was evidence of occupation by goats and their herders: a hearth, a rough wooden bench, some hurdles to pen the animals, and piles of their ancient droppings.

‘Welcome to the cave of the Cyclops,’ Aulus said.

‘They were sheep.’

‘Eh?’

‘Not goats, sheep. Odysseus and his crew escaped by tying themselves under the bellies of sheep.’

‘If you say so,’ Aulus said. ‘I don’t care for poetry.’

Valens remembered the lines where Odysseus escaped.

Dear old ram, why last of the flock to leave the cave?

In the good old days you would never lag behind the rest . . .

Are you sick at heart for the eye of your master

Gouged out by a coward and his wicked crew?

Valens put his hand on the hearth. The ashes were cold, but did not look as if they had been there very long.

‘The daemon appeared before Lucia and her husband left for Adiabene,’ Valens said. ‘This fire has been lit since then.’

‘Would get chilly up here at night, even in summer,’ Aulus said. ‘Maybe daemons feel the cold?’

‘That would account for their predilection for bathhouses.’

Aulus snuffled the dusty air. ‘No feral smell. No bear or the like has made this its den.’

‘Is that better or worse than a daemon?’

‘Maybe better.’

A passage opened at the rear of the cave. This was low, and they had to go on hands and knees.

To give him his due, Aulus did not hesitate to go first.