‘Ah, how I have missed you, scholar,’ Bolghai said, in his lightly accented Northlander. ‘Our talks of this and that, of men and stars, of the fate of the whole world and the precise shape of a grass seed, late into those long Northlander nights. But, as you may know, I have since commissioned some research into the biography of the great engineer Yu, who designed and built flood defences in Cathay some three thousand years ago. There are gaps in his biography, and I have come to suspect that he travelled in his youth – why not? And why not to Northland? Which was a great civilisation even then. I have come to suspect that the design of your mighty Wall could have sprung from Yu’s fertile mind. The similarities are striking when you consider such works as—’

‘Oh, now, you’re trying to provoke me! What a lot of nonsense. It’s far more likely that this upstart Yu came to Northland to study a Wall which was already ancient long before he was born . . .’

‘They’re good together,’ Uzzia murmured as she walked with Avatak. ‘Two bantering scholars. Pyxeas needs to make sure he doesn’t go too far, however. Even this Bolghai must have his Mongol pride.’

Avatak was staring up at the ceiling, at a panel where Mongol warriors on horseback shot tiny arrows at a rampaging dragon. ‘What a room this is.’

‘That’s what plundering a continent earns you.’

They came now to the scholar’s facility, and Avatak saw that it was a series of glass-walled compartments – domes, square-walled boxes, some a good deal taller than he was. Tubes of some flexible material led from each box to a complex apparatus of brass and glass, fussed over by attendants.

And in each of the boxes there was something alive, he saw. Something growing. A tray of soil bearing grass shoots in this box; in the next, what looked like wheat; in the next, potatoes; in the next, rice. These boxes were bathed with sunlight from open windows in the walls above. In the very largest boxes there were animals, one to each compartment: a horse, a cow, a sheep – a man, Avatak saw with shock, a small, skinny, youngish man of Cathay, sitting naked on a mat, his eyes averted, bowls of piss and shit beside him. Beside each container was a similarly sized box, quite empty, but fitted with tubes and valves. The largest dome contained a tree, of a kind unfamiliar to Avatak, with wide branches and bright green leaves, growing from a big ceramic pot. A tree, taller than he was, in the middle of this vast room.

Uzzia stared, amazed. ‘By the Storm God’s left buttock, what under heaven is this?’ Then she remembered herself, and she bowed hastily to Bolghai. ‘My apologies, lord. I am a simple trader; I am overwhelmed by this evidence of your mighty learning.’