They rode past the confluence of the Cyrus and Aragos rivers and followed the valley of the latter to the north. The Aragos was broad. It ran in several shallow streams, separated by low shingle banks. The green hills descended some distance away. Every so often they were cut by tributaries that came down in reed-fringed, wooded gorges of their own making.

At the end of the second day, they made camp just beyond where Ballista and Pythonissa had left the Aragos and taken to the hills in their flight to the east. From there, it took the army two days to reach the Dareine Pass. Now the hills were closer. Small figures could be seen on the higher slopes, watching them. It was impossible to say if they were Alani, or followers of Saurmag, or Suani loyal to Azo. Although in dribs and drabs, small numbers of the latter began to appear in the camp to perform proskynesis to Pythonissa. Some stayed to fall in behind her with their weapons.

As they progressed upriver, they were riding back over the ground where Ballista and Pythonissa had been pursued. They went by the ruined barn where the Suanian Kobrias had died so that they could escape. Ballista would have said a prayer to the Allfather for him, but that deity of the distant north had no interest in men from Suania. Ballista was unsure how much interest Woden had even in his own descendants.

At the Dareine Pass, Hamazasp invoked the oath sworn by Pythonissa. In that desolate place he installed a garrison of one thousand of his Iberians, under the command of his younger brother, the pitiax Oroezes. High on one of the bare shoulders of rock, they got busy pitching tents, setting out horse lines, building fires. The smell of the dung they used as fuel wafted down to where the army camped along the path in marching order.

Ballista sought out Tir-mihr. He spoke quietly in Persian. Since his involuntary use of that language in the paradise after the charge of the boar, there was no further point in reticence. ‘This is the main pass down from the Caspian Gates out of the Caucasus. Now the pitiax holds it, have we not put ourselves in Hamazasp’s hands?’

Tir-mihr inclined his head, a gesture acknowledging the force of the argument, but not accepting it. ‘If we lose, very few of us will escape these mountains. The Alani will hunt us down and the Caucasian tribes will turn on us: Iberians, Albanians, Suani – all of them. It will be a disaster like that suffered by the Achaemenid Cyrus at the hands of the Massagetae If we win, Hamazasp will not dare oppose us, nor would he have the power. But I imagine the king of Iberia thinks, as you did, that he has got the better of us. Mazda willing, he will be proved wrong.’

The army turned right out of the Dareine Pass and followed the Alontas river to the north-east. Ballista had ridden this route twice before – arriving in Suania and in his flight. It looked familiar, if far from welcoming. High above the slopes, eagles soared, riding the updrafts on wide, feathery wings. Many among the Caucasians made the sign of the evil eye or openly cursed them.

The army was moving with no great haste. It was settling in for the night when a Suanian galloped in from the north. The Alani were breaking their camp before Cumania, ready to move south. Already their scouts had been seen before Dikaiosyne. Narseh ordered Tir-mihr to take one thousand Sassanid horse ahead in a night march to the village. The main body would set out before dawn the next day to join them.

Breaking their camp before Cumania… the words reverberated in Ballista’s thoughts. Their camp before Cumania… the fort had not fallen. Do not tempt the gods but, most likely, Calgacus was alive; most likely Wulfstan and the others were too. Allfather, Grey-hood, Deep-thinker, let it be so, let the miserable old Caledonian bastard be alive.

It was raining as they rode into Dikaiosyne. The place looked no more prepossessing than before – tall, gloomy stone towers, narrow lanes and mud. There were hairy pigs and yapping dogs everywhere – under the horses’ hooves, unsettling them. As they crossed the village square, Ballista eyed the Mouth of the Impious. From Germania or Rome, this really was the far end of the world. They did things differently here: cursing eagles and protecting rams, sacrificing madmen and throwing adulterers into underground rivers, eating millet – no end to their strangeness.

Narseh quartered the troops then held a brief council of war. They stood on the flat roof of a tower, looking north. The Alontas was braided in several shallow streams. Its broad valley was rain-swept, its flanks bare, except for the two tangled ravines about half a mile away, where mountain streams came down, one on either side. A straightforward battle plan was outlined. Clibanarii and allied heavy horse in front. Narseh himself, Tir-mihr and the kings Cosis and Hamazasp would command. The light horse were to form up behind under the orders of Gondofarr. In both lines, the Persians would hold the centre, with the Albanians on the right, the Iberians the left. The topography dictated a frontal clash. The baggage was to stay in Dikaiosyne. With no danger of outflanking, just one hundred Sassanids would be sufficient to guard it from local banditry. It would be best if the mobad Manzik, the Romans, the kyria Pythonissa and her Suani remained in the village to oversee it. Tomorrow would bring the battle – let everyone get what rest they could.

Pythonissa led Ballista and the other three Romans to her house. After they had eaten, she took Ballista to her room. Beds were made for the others elsewhere. When they were alone, Pythonissa was eager, wanton. She tugged at Ballista’s clothes, pushed him on the bed, mounted him. Leaning forward, her breasts just above his face, she rode him, all the time saying the things that excite men.

Ballista woke in the middle of the night, sometime around the sixth hour of darkness. There was an odd smell, oily with a note of burnt almonds. Without moving, he opened his eyes. Pythonissa was not beside him. He sensed a presence in the far corner. Silently, he raised his head.

A single lamp was burning. Pythonissa was naked. She held his drawn sword. She was rubbing a liquid from a phial into the steel. Ballista watched her for a time. ‘What is that? Poison?’

‘No.’

‘Is it poison?’

‘No, it gives strength. It is what Medea gave Jason.’

Ballista grunted his disbelief.

‘You still wear the ice-white gem I gave you. Have your nights been disturbed?’

‘Coincidence.’

She laughed, walked towards him. ‘The unguent works on flesh too.’

‘You should have been a hetaira.’

‘You are not the first man to call me a whore.’

In the morning there was a thick mist. It haloed the many torches in the village square. Prince Narseh approached one of the huge panniers by the Mouth of the Impious. He drew an arrow from the gorytus on his hip. He dropped it in. One by one, the nobles and officers did the same. The clibanarii and light horsemen would throw in their arrows with less ceremony. Ballista knew from Herodotus that, long ago, the Persians had marked out an area of ground, marched in their men in their thousands. After the battle, they had repeated the procedure. From the empty space, they had estimated casualties. The new Sassanid system gave far greater accuracy. At the end of the day, every man took back an arrow. Those shafts remaining in the panniers indicated the number fallen.

An Iberian nobleman approached Narseh and performed lesser proskynesis; understandable, given the mud. ‘I bring bad news, Prince. The noble king Hamazasp sends his apologies. He has been struck down by illness. He is unable to ride with you to battle and share your glory. My name is Ztathius, son of Gobazes, I have been given the honour of leading the warriors of Iberia. Hamazasp will keep back only a hundred of his men as guards.’

The words of Ztathius were received in silence. Young Gondofarr looked openly sceptical. Tir-mihr scowled behind his beard. But there was little that could be done. ‘So be it,’ said Narseh at last. ‘Mazda watches you, and your king.’

With Pythonissa and the other Romans, Ballista climbed to the top of the tower where the council of war had been held. It must have been dawn, for there was light behind the mist. But the vapour was still thick, limiting vision to no further than a boy could throw a stick.

A trumpet sounded, muffled in the fog. A detachment of Sassanid horse bowmen trotted out below the tower. They disappeared north into the gloom, fanning out to screen the deployment of the main force. A drum began to beat. Below the tower, Narseh led out the clibanarii. At a stately pace, they manoeuvred into line. The Iberian heavy horse followed, taking their station to the left, then the armoured Albanians moved out to hold the right. The three thousand cavalry, eight deep, filled the valley like a phalanx of iron statues. Where they stood in the streams of the Alontas, the water swirled around the hocks of the horses.

At a trumpet call, the screen of bowmen trotted back through the narrow gaps between the divisions. The rest of the light horse rode out of Dikaiosyne to join them. Until the army moved forward, there was not room for all the four thousand unarmoured to take their places. Many were left still jostling in the lanes of the village.

The fog was thinning. Ballista could see a hundred yards or more. Below the great lilac standard of Narseh, he could make out the mobad Manzik. The priest was on foot, praying, arms raised. A white ram was being led up. With no warning, arrows arced out of the vapour. Most fell short. Some clattered off the armour of the clibanarii. A few landed near the sacrifice. The mobad took no notice. He pulled up the ram’s head, slit its throat. The beast collapsed. The priest again raised his arms and invoked his god. The arrows were falling thicker. Nomad horns howled in the mist. Manzik prostrated himself before Narseh, unhurriedly got up and, as if strolling in a peaceful garden, made his way through the ranks back to the village.