That night they again stayed in a way station.

And the next morning, soon after the start, when they passed over the crest of a hill, Regina glimpsed Londinium itself. The town was a marvelous gray-green sprawl of buildings contained within a far-flung wall. A shining river ran through it. Smoke rose everywhere, thin threads that spiraled to the sky. Regina thought she saw a ship on the river, a green-sailed boat that sparkled in the low morning sun, but she couldn’t be sure.

“Are we going on a ship?”

“No—child, I told you already. We aren’t stopping in Londinium. We’re going on. Don’t you listen?” Aetius seemed to be getting angry. But Carta put her hand on Regina’s shoulder, and he subsided.

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.”