Severa had been relatively happy here at Eburacum. Compared to the cities of the south, let alone Rome, it was a coarse, military-tinged place. But the officers of the sixth legion and their wives formed a seamless social circle with ties of patronage, obligation and letter-writing that stretched all the way back to Rome itself - a circle that excluded any British, of course. It was a circle Severa had immediately joined thanks to her friend Ceriala, and so she had restored contact with her own world. But now here she was enduring the goading of this buffoonish barbarian soldier, and her fury was obvious.

The trouble was, if the Wall was ever to get built they had to convince Tullio.

Tullio was prefect of the auxiliary troops stationed at the fort at Vindolanda, just south of the line of the proposed Wall. He was a Batavian, who had begun his career as commander of a unit of troops from that Germanic nation. Tullio had very visibly done well out of his career in the army. Through his service he had become a citizen, and a member of the equestrian class - Rome’s highest below that of senator. He had a handsome apartment here in Eburacum. He had even taken a wife, a dark-haired British woman. He was a walking exemplar of the fact that the army was not just a tool for subjugation and control, it was a machine for processing barbarians into serving soldiers, useful veterans and loyal citizens. And as the officers, senatorial-class, were merely working through military postings en route to more glittering career destinations, Tullio was possibly the most experienced soldier at Vindolanda, or indeed in any of the northern postings.

Now Nepos, who as governor was commander-in-chief of the army in Britain, had given this solid man a peculiar commission.

The Wall would be built by the legions, which, descended from Rome’s first soldiers, phalanxes of farmer-soldiers from the plains of Latium, remained the core of the army. All three of Britain’s legions would send detachments. Legionaries were trained in construction work, and each legion had its own specialist teams of engineers, architects and master builders. There was probably no workforce in the world better suited to such a mighty task.

But once built the new Wall would be manned, not by legionaries, but by auxiliaries. Some auxiliaries were infantry like the legions, but many were specialists: cavalry, slingers, archers. These days many auxiliaries were provincials, co-opted into the army for their special prowess. Auxiliary units were more suited to the rapid-response policing operations of a frontier fortress than the legions, who were trained for set-piece battles in open countryside.