Meanwhile more trains came rolling into the hub station from the habitat interior, laden with goods, foodstuffs, timber. The ColU speculated that some of these goods must be meant for export from the habitat, perhaps to other space colonies, as well as supplying the big hub cities.

At last the train pulled away.

At first the descent was alarmingly steep and rapid. Looking ahead, sitting on a wooden bench and with her head resting against a window, Mardina saw that they soon descended below the level of the cloud forest and into more open air. Now they emerged from the last foothills of the mountains and came to a flat plain – flat at least in the direction of travel – marred by ranges of low hills and gouged by the valleys of sluggish rivers. This land was the puna, the prefect said. The great plain itself was uninspiring, Mardina thought, as they sped across it, nothing but grass and shrubs on arid land. But if Mardina looked sideways she could distinctly see the upward curve of the landscape, as if she was travelling through some tremendous valley. Sparks of artificial light and palls of smoke on those sloping walls must mark townships, and she saw the iron glint of rail tracks and roads.

And there were people everywhere, farming the land in great fields and on terraces. The buildings they lived in were unassuming hut-like structures, although the larger townships featured complexes of massive warehouses that the apu said were tambos, imperial facilities for storing food. Every so often they saw a larger structure yet, compounds surrounded by walls with multiple terraces like huge steps. These were pukaras; they were obvious fortresses. Their walls were of a rough, dark stone that the ColU speculated might be rock from the dismantled moon.

But some features of the landscape were less recognisable, to a Brikanti eye. At rail junctions and springs, even on particular outcroppings of rock, there were small shrines that the Incas called huacas, with carved idols, poles, cairns, hanks of human hair – once, even what looked like a mummified human hand. It was as if the landscape was permeated by the presence of gods and spirits. Away from the sparse human settlements it was as if nothing existed on this eerie plain but the train on its track, and the markers of the gods.

Quintus had a conversation with the apu, steadily interrogating the little official about the nature of the world.

The ColU summarised this for Mardina. ‘This engineered landscape, the puna, is the equivalent of what was called the altiplano in my culture. In Valhalla Inferior, this was a plain of tremendous extent, very amenable to cultivation. And high, two miles or more above the level of the ocean. Just as it seems to be here, judging by the thinness of the air. Again they recreate their culture from Terra.’

‘But there’s so much of it,’ Mardina said. ‘It’s crushing. And what is it for? All these people labouring away, this gigantic engine they live in …’

Quintus joined them. ‘The apu is not a discreet man. Given a little flattery he has explained to me the essential purposes of this monster, this Yupanquisuyu.

‘It is the hub of a system of exploitation and expansion and control that spans sun, moons and planets – the Empire of the Four Quarters. The vast fertile expanses of the habitat feed the miners and engineers who work the worlds and moons across the solar system. The habitat is a source of people too, people to be trained up to mine those moons. And, as well, it is a recruiting pool for soldiers to fight the occasional necessary war – these days wars against internal rebels, since the Inca empire seems to span the whole planetary system. Oh, and the habitat supports the enormous establishment that sustains the Sapa Inca himself, son of the sun. Well, one must be seen to be wealthy and in control, mustn’t one? Our Caesars always knew that. Hanan Cuzco, his ghastly city in the airlessness of the hub, is the Sapa Inca’s Capitoline Hill …’

‘And there is one more objective,’ the ColU murmured. ‘One more purpose all this serves.’

Quintus nodded. ‘They have star vessels. Bigger than our Malleus, it seems, but no more advanced. They have many of them, in great fleets, which for more than a century, says the apu, have been swarming out to the stars, and—’

‘Building Hatches,’ Mardina breathed.

‘So it seems. On a far greater scale than we ever did.’

The ColU murmured, ‘And so it goes. Whatever the merits of this culture compared to any other, we can say one thing: it is better at building Hatches. As if it has been designed to serve the needs of those who would desire such a thing. And just as we would expect given our prior experiences of jonbar hinges.’

Quintus grunted. ‘Apparently so. But I would suggest we set aside such cosmic mysteries for now and focus on the needs of the present, which will be challenging enough.’

It turned out to be ten hours before the first stop – ten hours in fact before they reached the end of the altiplano. Since the ColU estimated that the train, running without a break, was averaging sixty Roman miles an hour, that gave Mardina another impression of the sheer scale of this artefact into whose interior she was busy tunnelling.

When the train finally slowed, night was falling across Yupanquisuyu. Mardina supposed they must fortuitously have been brought to the hub from space in the morning. She wondered vaguely how the mirror mechanisms worked behind the Inti windows, deflecting away the unending sunlight to emulate nightfall.

They got out at a waystation, which Ruminavi called a chuclla. Here there was a kind of refectory, and a place to wash, and shops where you could obtain food or even fresh clothes, and dormitory blocks – but the apu said they would not stay long before the train resumed its journey, with a fresh crew; they could sleep on the train, or not. Anyhow the grumbling legionaries had none of the credit tokens you needed to buy stuff at the shops. The Inca soldiers laughed at their frustration.

This small hub of industry and provision was set in the astounding panorama of Yupanquisuyu.

As the Romans bickered around the shops, Mardina once more walked alone, away from the station. Though by now it was evidently full night in the habitat, it was not entirely dark; the residual glow seeping from the light pools was clear and white, but so faint that colours were washed out. It was like the moonlight of Terra, Mardina thought, and no doubt that was by deliberate design. She could make out the sleeping landscape all around her, the terraces and fields. A little way ahead, though, the country began to break up into hills and valleys that were lakes of shadows. They would be descending soon, then, to lower country, and thicker air.

And to left and right the uplift of the landscape was easily visible, even in the night. The ColU had told her that a round world with the curvature of this cylinder would have a horizon only a mile away, compared to three miles on Terra. So, well within a mile, she could see the land tipping up, the trees and houses visibly tilted towards her. And the rise went on and on – there was no horizon, only the mist of distance – until the land became a tremendous slope, bearing rivers and lakes at impossible angles. Soon the detail was lost in darkness, and in the thickness of the faintly misty air. But then, as she raised her eyes further, she saw the roof of the world, an inverted landscape glowing with pinpricks of light. It looked like the dark side of Terra as seen from space, with threads of roads and the spark of towns clearly visible beyond its own layer of air and clouds. At this altitude the air was so clear it was as if she was looking through vacuum.