The governor, a practical man, saw the need for a ‘foreman’ accountable to Nepos himself to oversee the project. As an auxiliary commander Tullio would not command any of the legionary detachments who would build the Wall. But as it was his troops who would use the Wall, Tullio had a vested interest in making it work. And so, wise councils had agreed, Tullio was just the man for the job.

The trouble was, here was this competent, trusted man laughing Xander’s precious scheme out of court.

Karus stood grandly. ‘Gentlemen, this is an imperial commission. We all have an interest in fulfilling that commission. And you are scarcely being respectful to the lady. Let’s have a little gravity, shall we?’

The ploy seemed to work, and Tullio calmed down. ‘All right. And you, Butimas, if you swallow that fort you’ll be for it!’ Tullio aimed a kick at his sons, who fled, laughing at their own jokes. Tullio turned back to Xander. ‘Sorry, friend. Try again. Sell me this Wall of yours.’

Trembling a little, Xander restored his increasingly battered model, and turned to a folio of sketches on parchment. ‘Here is the Wall itself. Fifteen feet high, ten wide. A foundation of slabs in clay, then two courses of dressed sandstone around a core of clay or cement. In front of the Wall - that is, on the north side, facing the barbarians - you will have a berm eighteen feet wide, and then a ditch, shaped like a V, you see? Twenty-seven feet wide, ten deep, with a drainage channel cut into the bottom.’

‘And this thing will cut right across the country, yes?’

‘Yes. Local streams will be culverted through the Wall. Over significant river crossings we will need bridges.’

‘Bridges, of course,’ Tullio said, still mocking.

The aide, Annius, said cheerfully, ‘And on top of this you want forts and turrets, I suppose.’

‘A fort every mile, with a gate, and two turrets set into the curtain wall between each pair of forts. I have the drawings here ... The Wall will be plastered and painted white.’

‘Oh, very nice,’ said Annius.

‘Such an edifice laid across the neck of the country will be an imposing statement.’