The ship out of Carthage took them west, through the strait into the Western Ocean, and then to a Carthaginian port in southern Ibera, at the mouth of a mighty river. The port was working, the harbour crowded with shipping, the town itself bustling. But Avatak, having seen a dozen ports on the way back home on the Arab trader, had learned how to read a town, a countryside. He quickly saw that the ships were bringing in food, armour, other supplies, and they were taking out people, more nestspills, all heading south. The country that had once sustained this port had become a threat to it; the landward city walls were heavily armed against rough camps of nestspills beyond. But that was the country across which they must travel.

They spent three days spending Carthaginian money on what they needed for the next stage. They hired a riverboat to take them deep into the interior of the country, and a troop of the port’s city guard for protection. Their elaborate carriage was loaded on board the boat.

They sailed out beyond the protection of the city walls by night, to minimise the threat from the great band of nestspills, bandits and warlords that surrounded the walls. The weather inland was cloudy, blustery, cold, and it frequently rained, the water pooling on the hard earth. The soldiers from the coast huddled under leathers and gambled over games played with broken bits of bone. Pyxeas spent much of his time working in the little shelter on the carriage, or dozing.

They passed by empty towns on the riverbank, and huge plantations where once olive trees had grown in great numbers.Now it was all gone, the weather too wet and cold for the olives, the people bankrupted, fled or starved. But the land was not barren, Avatak saw; in places swathes of grass glowed green in the rare sunlight. Nelo sketched all this compulsively, on Egyptian paper scraped so thin you could almost see through it.

Pyxeas, on one of his rare ventures out of his tent, nudged Avatak in the ribs. ‘Remember the steppe? One day soon, it may only be centuries, this place will be an ocean of grass too, just as we saw in the heart of Asia. The great-grandchildren of these boatmen and laughing soldiers will be horse-riding nomads, and herds of fleet beasts will cross these plains like the shadows of clouds. I, Pyxeas, predict this.’

Himil looked baffled. ‘I do not question your conclusions, scholar. But how can you know all this?’

The scholar smiled and tapped his temple. ‘From observations of the world – from patterns deduced, and stored in my memory – from understanding the superhuman rhythms of the ice.’

Himil just stared. Then, when the scholar had withdrawn, he turned to Avatak. ‘You must know what he’s talking about.’

Avatak shrugged.