But, watching the Wall rise grandly over the crags, Brigonius wondered how much this military theorising mattered compared to the brute physical reality of the Wall. It was a monument to the power of the Roman mind like nothing ever seen before in Britain - or, according to Tullio, in the whole world - and even if it were not manned by a single soldier such a structure would surely deter all but the most fanatical enemies of Rome.

But then, Brigonius reminded himself, despite certain harm done to him, he was not a fanatical enemy of Rome.

Brigonius arrived at his own limestone quarry. This was a great scoop out of the south side of a hillside, not far from the line of the Wall, some miles to the east of Banna. He rode up from the north, so he could stand at the lip of the artificial cliff that had been cut into the crag and view the activities in the pit. Long lines of men snaked from the quarry face to massing points by the carts, lugging stone. They were the men of the sixth legion, mostly drawn from Gaul and Germany but some from further afield. Day after day they hacked into British limestone, roughly cutting the stone blocks and dragging them to the carts to be hauled off to the construction sites.

The speed of the work was remarkable here too. In less than a full season’s working the quarry had already been hugely extended, following the seam of rich creamy rock, from the small bite into the turf-covered crag that Brigonius had inherited. The legionaries had a variety of specialist tools that Brigonius coveted, such as heavy hammers, steel-tipped wedges and crowbars, and cranes for lifting heavy blocks. In one part of the quarry a watermill worked a trip-hammer, flailing arms which battered at intransigent rock. He had heard a rumour that in another quarry further along the Wall stone was being cut by a water-driven saw.

But in the end it was brute labour that was getting the job done. Even from here Brigonius could see how the sweat glistened on the backs of the legionaries as they toiled. The Wall would be seventy miles long, and somebody had to cut out every single block of stone, haul it to the Wall line and mortar it in place.

‘Brigonius.’

He turned. Here was Matto, his cousin, a stocky man ten years older than Brigonius. Matto was black-bearded, dark-haired, and he wore a heavy woollen coat dyed deep blue-black, so he was a knot of darkness in the middle of a bright summer day. It was hard to imagine a figure more anti-Roman in his style.

‘Cousin. You crept up on me.’

Matto grinned, and Brigonius saw yellow-brown quarry dust embedded deep in his pores. ‘Just as you sought to creep up on us - eh?’