They turned their backs on Londinium, heading north. Regina looked back at the city as it receded. “I’ll go there one day,” she said. “I’ll go far beyond it, too! I’ll go all the way to Rome!”

Aetius grimaced, and hugged her with his massive arm.

For Regina, after the city, this third day turned out to be the most difficult so far. The sky lidded over with gray cloud, and although the sun was gone the temperature rose steadily. They were all soon sweating uncomfortably, and they had to stop frequently to allow the horses to drink.

Aetius, apparently trying to compensate for the absence of Regina’s tutors, chose this difficult day to lecture her on the essentials of Roman Britain.

Britain was a diocese within the Praetorian Prefecture of Gaul. So the vicarius, the governor of Britain, reported to the prefect of Gaul, who reported to the Emperor. Similarly there was a hierarchy of towns, from the lesser market towns, up through the local and provincial capitals, to Londinium, the capital of the diocese.

The most important activity of the central administration was the collection of taxation and the spending of government funds. Most of the tax money came from the countryside, because that was where most people lived. Landlords, like Regina’s father, collected the Emperor’s taxes from his tenants, along with his own rent. The tax revenue paid the salaries of the army and the sailors of the British fleet, who kept Britain safe from the barbarians who would otherwise swarm from the north and across the sea.

People grumbled about the taxes they had to pay. But most of the money collected came back into circulation. And the fact was the vast volumes of foodstuffs, animals, clothing, metalwork, pottery, and other goods bought by the government to supply the army and its other agencies was central to the working of the economy …

Aetius struggled to explain: “It’s like a wheel, Regina. It goes around and around, a great wheel of money and goods, taxing and spending, keeping everyone safe and wealthy. But if a wheel comes off its hub—”

“We’d fall over.”

“Exactly. Everything would fall over. Now then, when my old chum Constantius took us soldiers away for his adventure in Europe, some people in the towns decided they didn’t need to pay his taxes anymore, and threw out his collectors and officials, and said they would collect the money for themselves and keep it for their own towns, rather than give it all to some distant Emperor they never saw. But while people will pay up for an Emperor, especially if he has an army to collect for him, they’re a lot less willing to pay some fat fool of a local landowner …”

Regina was a bright child, and capable of understanding a great deal. But at seven she was an experienced enough student to know that while Aetius might be a fine soldier he was no teacher. He was boring.

And as the day wore on and the heat continued to stifle, Regina got more and more uncomfortable. It had been days now since she had seen her mother. Aetius never mentioned Julia, and Regina was wary of asking. She missed her mother even so, and wondered where she was. She grew withdrawn, sullen.

Eventually Aetius relented and let Regina sit in the back with Carta. They tried to play ludus latrunculorum — “soldiers,” a fast-moving game a little like chess played only with rooks — but the rattling of the carriage knocked the colored glass counters away from their squares. So they settled for par impar, a simple game of odds and evens, played with pebbles held in the hand.

That night they stayed at yet another way station. The next day they made another early start, but Regina found it increasingly hard to sit still.

Things came to a head when, about midday, the weather abruptly broke, and an immense storm lashed down from a gray lid of sky. Aetius insisted they kept going, but soon they were all soaked through. Regina was cold and frightened; she had never been exposed to such elemental rage before.

When the storm finally let up she pushed away from Aetius and jumped down from the carriage. “I won’t go any farther! I want to go home, right now! Turn around and take me home! I command you!”

Aetius was angry, placating, demanding, but he got nowhere; and when his will broke against her seven- year-old stubbornness, he stomped around the road, fists bunched.

Cartumandua, with some courage, intervened. Soaked herself, she clambered down to the road surface and brushed at Regina’s hair, calming her down. She said to Aetius, “Sir, you can’t speak to her as if she’s one of your legionaries. And you can’t expect her to sit there day after day on that wooden bench and listen to you lecture about procurators and prefects.”

“She needs discipline—”

“It’s not natural. You need to give her time.”

“But every heartbeat we stand here in the road is wasted time.”

“The Wall has stood for three centuries, and I daresay it will still be there if we take a few days more. If you don’t make allowances, I don’t think we’ll get there at all.”

He walked back grudgingly. “Catuvellaunian princess or not, you are a feisty one for a slave.”

She dropped her head submissively. “I’m just trying to help.”

Aetius crouched down before Regina. “Little one, I think we have some negotiating to do …”

They continued the journey, but after that to a different pattern. They would ride a while, and break a while, generally long before Regina got too bored or uncomfortable — although Aetius retained the right to keep on if he was ill at ease with the countryside, or the company they kept on the road. Their pace dropped, from fifty or sixty waystones a day to less than forty.

But for Regina, though she lost count of the days, and had only the dimmest idea of where they actually were by now, the trip became much easier — even fun again, as the days settled into a new routine.

As they worked steadily north the countryside changed character.

Though the road still arrowed past farmsteads, there were far more roundhouses of the old British type, rather than the rectangular Roman-style buildings. The towns here were more like bristling forts, with tall walls and looming watchtowers. Here and there Regina saw plumes of dust and black smoke rising up. Aetius said they were mines. Once they passed a man driving muzzled wolves along the road; he was a trapper, hoping to sell these animals to a circus.

In the roadside dirt Aetius sketched a map of the island of Britain, and slashed a line from southeast to northeast, from the Severn to the Humber. “Southeast of this line there are plains and low hills. Here you’ll find fields and citizens, with everything run from the towns — under the greatest town of all, Londinium, capital of the diocese. Northwest of this line there are mountains, and barbarians, and tribes and chiefs who run their own affairs and have barely heard of the Emperor, and pay his taxes with the utmost reluctance. To the southeast there are a thousand villas, but none at all in the northwest. That is why, to the northwest, the diocese belongs to the army.” But Regina continued to have only a dim grasp of the country’s geography, or indeed of where they were.

In the final days, as the endless northward journey continued and they rattled across high, bleak moorland, Aetius told her something of his family’s past.

“We were all Durotriges. Your father’s people were aristocrats — landowners — even before the Romans came,” he said. “ My people — and your mother’s — were farmers, but they were warriors.” He glanced back at Cartumandua. “The Catuvellaunians call themselves a great warrior people. But when Claudius came they rolled over and bared their arses to him …”