Thalius ambitiously tried to explain to Audax the difference between ‘finitude’ and ‘infinity’. Audax’s deep confusion came from a life spent in the enclosed and finite, and now he was stranded in a world of openness without end. Audax dimly grasped these ideas. But he thought it just went to show that Thalius had never been a slave. Slaves understood infinity, even if they had no words for it, for slaves faced a lifetime of labour, of an utter lack of choice, without end. Servitude was infinity.

The one element in this huge open world of the outside that he felt drawn to was the sun. When the sky was clear the warmth of that great lamp in the sky sank deep into his bones and drew up his blood. Thalius gently explained to him that it was the sun that gave life to all things on earth, and that some people worshipped it as a god. Some believed it was a form of Thalius’s own god, the Christ, who had also been a man. The sun reminded Audax of Tarcho, in his strength, his warmth, his patience. Audax imagined Thalius’s Christ as a huge bearded soldier in the sky who smelled of sour German cabbage.

They stayed a couple of nights at a place called Eburacum. This was a city of massive walls and towers strung along a riverfront, looking down on the civilian town that huddled around it. A huge building loomed out of the centre of the town, visible for miles around. It was the Roman military headquarters, Tarcho said.

Founded as a legionary headquarters Eburacum had always been an important place. One emperor had died here: Severus, a century ago, after his campaigns in the Highlands, and after making Eburacum capital of one of his two British provinces. Since then the fortress and its walls had been rebuilt, massively. And another emperor had been created here, in Constantine, who had been proclaimed in that imposing headquarters building. Now Eburacum was the base of the military commander of the north, the Duke of the Britains.

But Thalius didn’t like the place. ‘With its aloofness and arrogance and monumental military architecture,’ he said, ‘it prefigures in stone the haughtiness of the absolute monarchy of the future.’ Audax didn’t think even Tarcho knew what he was talking about.

Travelling further north still they passed through more hilly country. The sky was huge and full of immense clouds. Somehow Audax found this wilder, more rugged landscape less intimidating than the crowded hills of the south. Thalius gently pointed out that this country was Brigantia, Audax’s home. But none of Audax’s ancestors had seen home for generations.