Karus and Xander had of course heard every word of the exchange. Karus, trying to cover the tense silence, rubbed his hands together. 'Well, as for me I could do with a shit, a bath, a drink, and some food, not necessarily in that order.'

Xander snorted. 'For a lawyer you're very crude sometimes.'

'That's the Brittunculus in me,' Karus said cheerfully.

Severa extracted a letter from her purse and unfolded it; the bindings of the wooden pages creaked softly. 'I have an invitation from one Ceriala Petilia, the cousin of a friend's friend, who just happens to be the wife of a tribune. She has offered to host us while we are here. A good Roman woman. No more barbarians!'

'Then all we have to do is find her,' Karus said mildly.

Severa glanced about and saw a soldier crossing towards the gate. He was a centurion, as Brigonius could tell from the vine stick he carried. 'You! Come here. I have an assignment for you.' And to Brigonius's astonishment she ordered a centurion of the sixth legion to carry her bags as if he was a common slave. Meekly he obeyed.

'Marvellous,' said Karus, but he sounded uneasy.

'Let me get this straight,' said prefect Tullio. 'You want to build a wall.' A brisk, bustling man of about forty with a shock of bright red hair, he was clearly used to command, and he easily dominated his cluttered office in Eburacum's headquarters building.

Xander, his model set out on the floor of Tullio's office, sat more nervously, Brigonius thought, than in the presence of the Emperor himself. 'Yes, a wall,' he insisted.

'Seventy miles long.'

'Seventy-one actually.'

'With three legions.'

'Yes.'

'And you want to do this in three years.'

'Yes.'

Tullio's eyes bulged. 'Are you twisting my cock?' He leaned back and called through the door. 'Hey, Annius! Get in here and listen to this. You'll love it.'

Another soldier, evidently one of the prefect's aides, walked casually into the office, polishing a strip of breast-plate armour with a bit of leather. He was a muscular man whose head was shaped oddly like a bucket, Brigonius thought, with a narrow chin, protruding teeth, a broad forehead and a mass of black hair. 'What's up, Tullio?'

Tullio turned back to Xander. 'Go on, friend. Do your routine again. How many miles? How many forts and turrets?…' As Xander stammered out his plan once more, Tullio and his pal leaned back in fits of laughter.

To compound Xander's mortification two small boys came running into the room, squealing. They both had red hair as bright as Tullio's. They had been playing with short wooden swords, but when they saw Xander's toy wall with its tiny fortresses and plaster hills they fell on it with delight. Xander, in a fussy panic, tried to keep the boys away, but he only excited them further and made things worse.

Amid this chaos Brigonius glanced around at his companions. Karus looked as if he was having trouble not laughing himself. Severa, however, seemed ready to burst into flame.

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.

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.'