Xander described the route he proposed. His mighty Wall would be rooted in the east, at the site of a small fort called Segedunum. It would cross the river Tinea, and then climb to the west following the high ground. Hilltops and a natural escarpment of basalt crags would be incorporated into the new frontier. ‘It will seem to all,’ Xander pronounced, ‘as if the Wall has sprung out of the very rock itself!’ Beyond this point would be a further river crossing, and then the Wall would take a less dramatic course through more broken country, finally crossing a plain and approaching its destination at the west coast. The total length would be some seventy-one miles, said the architect, every foot of which would be dominated by a stone curtain fifteen feet high. Not only that, earthworks before the northern face of the Wall would give further protection. The Wall would be punctuated by small fortresses, one every mile, and broken further by turrets, two between each pair of mile-forts, to provide signal points and massing positions. There would be gates in each of the mile-forts so that the Wall could be made as permeable or as closed as local commanders desired.

There could be no doubt that the Wall would be a magnificent piece of engineering, and Brigonius could see that Hadrian and several of his courtiers were immediately taken by Xander, his beautiful model, and his compelling vision. But others raised objections.

The first to speak was Aulus Platorius Nepos, Britain’s new governor. He pointed out some of the practicalities of building this monument. Under Hadrian in Britain there were three legions and sixty-five auxiliary units, some fifty-three thousand men in all. All three legions would be devoted to building the Wall - say fifteen thousand men. Nepos swept a hand over the model. ‘But all of this must be completed in three years, no more. My question to you is - are you sure of your calculations? Is this feasible in the time with the available manpower?’

Brigonius thought he understood why three years; a governor’s term was usually no longer, and Nepos would surely want to see the Wall finished during his tenure. But Xander seemed shocked to hear this time limit; his mouth opened and closed. Recovering, he stood his ground and spoke clearly. ‘We Greeks are famous for our arithmetic skills. I can assure you, sir, my calculations are sound.’

The next attack on the proposal came from a legate, the commander of one of the three legions currently stationed in Britain. He spoke of the border control that had already been set up under Trajan, along a line a few miles south of the proposed wall. Here, well-established forts, including Vindolanda, and connected by a good road, already served as a base for a rapid and flexible response to any trouble. Wouldn’t it be better to reinforce that existing barrier rather than to start afresh?