The lodgings obtained – an upper room of a tower, the floor of a barn – matched the young in filth. The thick, dark smoke from the fires of moss and pine chips did nothing to discourage the biting insects. At least the food, although monotonous, was wholesome enough: roast mutton or pork, boiled fowl, the meat on flat bread, washed down with goatskin-tasting wine.

Further into the mountains, there were fewer trees: here a sheltered slope of firs, there an upland pool ringed by maple and beech, the occasional, isolated birch. But up there the flowers had come into their own: thick tangles of cream rhododendrons shot through with purple, and banks of yellow azaleas perfuming the air. Underfoot, the turf was enamelled with lupins, bluebells and cowslips.

There were still habitations in the higher reaches. But the party had mainly passed by those lonely, closed-in towers, stark up on their ridges. The locals had likewise ignored them. Ten heavily armed travellers – now the slaves were armed too – might have been a bit too tough a target. The party had camped where seemed good in the open: flattish spaces, as far as possible, with a view all around. It had been cold in the tents, and every night some lost sleep, as a watch had to be set.

It was healthy. So Ballista had claimed. Clean, fresh air, aromatic fires of rhododendron stalks and roots, trout caught by hand in the backwaters, flatbread toasted on the blades of their daggers. Ballista’s slave Agathon was developing into a fine camp cook. Hippothous had not been convinced. The most elementary knowledge of medicine indicated that water from snow and ice was very bad for one; the light, sweet, sparkling part vanished when frozen and did not return. Drinking from these icy upland streams could only lead to gravel in the kidneys, stones, pain in the loins, and eventually rupture. Only Calgacus seemed to give his gloomy prognosis much credence.

One morning, the thick, thick mist had lifted suddenly, and there was the big mountain, still far away, seen beyond a jumble of boulders and between the green shoulders of its lesser brethren, but incredibly massive, snow covered and solitary. ‘ Strobilos,’ the guide had said. ‘Where Zeus chained Prometheus.’ The mountain shone in the sun. In a moment, the mists had returned, and it was gone.

In the clinging, grey vapour, they had been walking up from a deep, green basin. A vague, tall shape shambled down out of the fog. Ballista and the others stopped. Bears were said to be common. They had drawn their weapons. Maximus had actually grunted with anticipation. The fog swirled. In it, the bear had started singing. Realizing it was a man, their guide had said something incomprehensible, and made the sign of the evil eye. The man came forward. Even by the standards of the mountain men, he was ragged and soiled. His body was emaciated. He was bleeding freely from several cuts and abrasions. His clothing appeared to consist of a stained, torn sack. The man had looked closely into Ballista’s face. There was no comprehension in his eyes. He stank. The guide had given the creature food, spoken gentle things to him. ‘One taken by the moon goddess Selene,’ the guide had explained. ‘When the servants of the goddess find him, he will live like a lord for a year.’

‘One year?’ Ballista had asked.

‘One year.’

‘And then?’

The guide had not answered.

They had left him where he was, and continued to climb. Their breath plumed. There was much snow still lying at the top of the pass. They descended via a steep slope of shale. Near the bottom, the mist had lifted again. There were yellow flowers in the grass. Ballista looked back. The locals had been avaricious. A Caucasian pony, even a nimble-footed horse could have made the crossing. No need for two guides and a dozen porters.

In front of them was the upper course of the Alontas river. It braided itself in many tiny channels across a broad, flat valley bottom. The rivulets twisted and turned. Banks of mud and stones were left exposed, each neatly curved, as if by the hand of a skilled potter. They were grey amid the prevailing lush green. The valley walls were precipitous and high. They were green, but bald, not a tree in sight. Here and there, they were riven by deep gullies. On the side of one, not far ahead, clung a grey village. There were horses and cattle grazing the flat pastures below it. It offered a chance to get in the saddle again, and the pleasure of dismissing all the grasping guides and porters.

A mile or so beyond the village, and the valley had turned. Another long valley, and then another turning. In the distance, more valley walls, higher and higher, fading from green to blue to misty grey. The ten small figures on horseback were dwarfed by the immensity. It did not matter; from that point, they had known all they had to do was follow the river and it would lead them to the Caspian Gates.

The Suani warriors were waiting for them here outside the last village before the Gates. There were thirty of them, mounted, spread out. They completely blocked the width of the valley floor. Some of the horses were in the various streams, hock deep. These drank or stamped and shook their manes as the mood took them. The men were well armed. Mail showed under the empty-sleeved Caucasian fur coats they wore loose over their shoulders. Some had metal helmets. Each had a lance or javelin in his right hand and a targe strapped to his left arm. From each saddlebow hung a combined bow case and quiver. They sat their horses well. They looked tough, if wild and ill disciplined.

Ballista wondered just how much danger he and the others were in.

The Suani rider with the most elaborate embroidery on his coat and on the gorytus suspended from his saddlebow paced his mount forward. ‘Which of you is Marcus Clodius Ballista, the envoy of the basileus Gallienus?’ The young man spoke in Greek. His words were moderately polite, but his tone arrogant, bordering on hostile.

Ballista nudged his horse out of the group.

‘Dismount.’ The order from the Suani was peremptory.

‘Who are you?’ Ballista kept his voice very level.

‘I am Azo, son of King Polemo of the Suani. My father is in the village. He is with the synedrion. They are expecting you. It will be best for you if you have brought the tribute.’

Ballista did not reply. He swung down from the saddle, indicated for the others to do likewise. He told them to break out the first two parcels of gifts. Calgacus was to stay behind with the horses and the remainder of the baggage, Agathon and Polybius with him. The rest were to accompany Ballista.

Azo and some of the Suani dismounted. Those now on foot set off up into the village. The others stayed where they were.

Dikaiosyne the village was called, ‘justice’ in Greek. When Ballista had asked why, Mastabates admitted he had no idea. The place had another, native name. The eunuch had not known what that meant either. Ballista did not think it the moment to question the Suanian prince Azo on etymology. They walked up in silence.

The first buildings began a good way up from the floodplain. They were built on a thirty-degree slope. Dikaiosyne was backed by a sheer rockface, which reared up several thousand feet. Above the settlement there was snow in every declivity. They trudged up the usual muddy alleys formed by the blank outer walls of compounds. Hairy pigs grunted out of their way. Dogs barked.

They emerged into the village square. It was full of people, some two or three hundred, stood in an inverted U, the open side towards the newcomers. Ballista tried very hard not to appear surprised; tried to take in his surroundings. The square was wider than most; small alleyways opening off from the otherwise featureless walls all around. It had at its centre not an old oak tree, but an oversized circular well. Next to the well was an eastern type of altar with a lit fire.

It was easy to pick out King Polemo from his advisors and subjects. He was seated in the middle on a high throne. A dark-bearded, sharp-faced man in middle age, he wore a cloak and turban, both white with gold thread, both a little grubby. His sword belt, scabbard and red boots were set with what looked like pearls. By one of his hands stood a younger, lighter-coloured, less impressive version of himself – that must be Saurmag, the other prince. On the other was a tall, blond, statuesque young woman – the troublesome daughter Pythonissa, the priestess of Hecate.

The members of the synedrion of Suania stood in the front rank. The councillors tended to be tall, well-formed men with aquiline, attractive, if hard, faces. In their dress they followed their king: a mixture of western styles – tunics, trousers and boots not unlike an unarmoured Roman officer; with barbarian – eastern turbans or nomad caps with lappets. From what could be seen, the warriors in the rear ranks appeared to favour cheaper, rougher versions of the same. None of them seemed to have an obsession with the baths.

A group off to one side caught Ballista’s eye. There were six of them. They were different – darker hair and beards, taller hats and baggier trousers, cleaner. They were not Suani. They were Persians – Zoroastrian priests. Of course, that explained the fire altar by the well. Ballista had been told by Mastabates that the chief of the Sassanid king’s fire-worshipping priests, none other than Shapur’s close confidant Kirder the Herbed, had led a mission of conversion to the Caucasus. Numerous fire altars had been founded throughout Albania, Iberia – across the whole region. Ballista looked hard. None of these men was Kirder. He had seen him once in Edessa. None of them was Hormizd, the Persian boy chance had briefly made Ballista’s slave. Ballista would not recognize any other Zoroastrian priests. The mobads in this village square looked annoyed. It made Ballista again wonder how strong diplomatic immunity would prove among the mountaineers of the Caucasus.