Maximus’s progress was slow. He worked small chunks of brick and timber along his body with his fingers and toes, pushed them out behind him. Eventually, his feet disappeared.

Ballista waited, playing out the makeshift, woollen rope. Calgacus was silent beside him. There was a faint but definite smell of burning. Up above, in a clear blue sky, the swallows wheeled and darted.

For a long time the rope did not move. Ballista could hear Maximus grunting, scrabbling, coughing. Every so often the nearby sharp crack or groan of moving rubble made both the watchers jump.

At long, long last they heard Maximus returning. Calgacus leant into the fissure, dragging out the rubble as Maximus booted it. Maximus’s feet reappeared. As he wriggled out, the sound of crying squalled after him.

Maximus slumped down. All across his body, bright-red gashes showed through the dense paste of sweat and dust.

Calgacus reached in and, like some nightmarish midwife, brought the child into the light. He passed Simon to Ballista, and leant in again. As tenderly as he was able, Calgacus pulled Rebecca out. The ugly old man cradled her in his arms.

‘Constans is in there,’ Rebecca croaked. She could hardly speak. They had not thought to bring any water. She disengaged herself from Calgacus, and took up Simon.

Ballista looked down at Maximus. The Hibernian nodded, an expression of much doubt on his face.

‘Calgacus, take them down to the others.’

Ballista helped them up to the lip of the hollow. Below, Julia and Rhode, Dernhelm on her shoulder, were in the open. For some reason, Hippothous was leading Isangrim apart, back behind the facade of the little temple.

‘Calgacus, get Isangrim and that Cilician fool back out of that death trap. And you take care on the way down.’

Calgacus waved a hand in response.

At the base of the depression, Maximus sat, eyes shut, panting like a dog. It was stupid not to have brought water.

Ballista’s hands went to untie the improvised belt at Maximus’s waist. He resisted the half-hearted attempt to stop him. ‘You are all done.’

‘Sure, it will not work.’

‘Maybe, but what can you do?’

With the rope around him, Ballista lifted his torso into the opening. Straightaway, his own body shut out most of the light. Awkwardly, he dragged himself further in. When his feet were in, he stopped. He lay still for a time, telling himself he was allowing his eyes to adjust. He tried not to think of the crushing weight of the unstable rubble above and all around him, tried not to let the terrifying constriction of his movements enter his mind at all. The tunnel was little wider than his shoulders, all its surfaces rough and catching. He wondered if he could carry on.

Like an animal with its back legs broken, he dragged himself forward with his arms, feet flippering ineffectually behind. A jagged piece of rubble sliced through his tunic. He felt the warm blood smearing his stomach. He let the pain rise; concentrated on that, used it to blot out the fear.

The deeper he went, the faster and shallower his breathing became. The air might be getting bad, or it could just be him. Keep going. Do not think, just act.

The ghastly tunnel opened out just a little. His hands, as much as his eyes, told him there was a lintel or the like overhead. It must have saved Rebecca and Simon. Beyond, the space felt no bigger than a rabbit hole.

‘Help.’ The voice was soft, but shockingly close.

‘Constans?’

‘Help! Zeus, it hurts.’

Ballista could make out something pale in the near-total darkness in front. He reached out. It was a hand and forearm; warm, gritty to the touch. They extended out of the rubble.

‘Constans, can you move?’

‘Zeus, Athena, all the gods, get me out of here.’

Ballista was finding it hard to breathe. He forced himself to talk soothingly, as he would to a horse. What he said he did not know. Slowly, not to startle him, he let go of Constans’s hand. Ballista ran his fingers over the rubble, trying to form an impression of what was there.

The opening was indeed little bigger than a rabbit hole. Ballista slid his arm in alongside that of Constans; there was next to no room for anything else. He patted the trapped man on the shoulder. Above the hole seemed to be one large block of masonry. With no equipment and no room to work, it would be impossible to break it up or move it. Below the fallen material was more fragmentary. Possibly it could be dug out, but then the unsupported block above would come down.

Ballista lay still again. His breath came in short gasps, making staccato the platitudes he continued to address to Constans. Ballista was not nearly deep enough for the air to be foul. As he talked, he thought about this specific tunnel. He thought about tunnels in general. His mind went back six or seven years, to Arete. Discussing with his friend Mamurra how best to ventilate tunnels. Mamurra, the friend he had left to die in a tunnel. There had been no choice. The Persians would have broken in, killed everyone. No choice at all. But, at times, the moment he had ordered the pit props knocked down, had the entrance caved in, came back with a horrible clarity. Not then, but later, the Persians had broken in anyway. They had killed everyone they caught.

A sharp tug on Ballista’s waist, then another. The northerner lay waiting – maybe he had missed the first pull on the rope. He said something to Constans; something reassuring, nothing valedictory about it at all. Ballista started to move backwards.

At first, he moved slowly, not wishing to unsettle Constans. Then he realized this was madness. Hands, elbows, knees, feet working furiously, he propelled himself away. He felt the sharp things; the abrasions, nicks and cuts blossomed all over his body.

Maximus caught him as he shot out feet first. The Hibernian set him down. Ballista was retching, wiping his eyes. They should have brought water.

Maximus pointed to the side of the depression. Smoke issued from at least a dozen vents. One streamed out in a jet, as if from a crack in a charcoal burner’s stack. Another gave out distinct puffs, like an angry chthonic god signalling catastrophe.

‘We cannot leave him,’ Ballista said.

Maximus nodded, hoisted himself into the opening.

Ballista knew what Maximus was going to do. Should he stop him? Ballista drew back from the abyss of the huge moral dilemma. He looked over the ruins; perilous and transitory. Ballista shut his eyes.

There came the sound of scrabbling. Maximus was back. He got out, re-sheathed the knife.

‘Time to go.’

III

‘ Dominus, have you decided what to do with Ballista?’ At the words, a silence spread through the dining room of the requisitioned house in Byzantium.

The Roman emperor, the pious, invincible Publius Licinius Egnatius Gallienus, did not respond to his a Studiis. The responsibilities of Voconius Zeno were to aid the emperor in his cultural studies, duties which did not stretch anything like so far as this.

‘The man has killed a pretender, had the temerity to assume the purple, even for only a few days,’ Zeno continued.

Gallienus selected a pear from the low table by his couch. Who has bribed you? he thought. How much did this question cost?

‘Ballista is in Ephesus, waiting for the start of the sailing season to take a boat and return to Sicily. In five days he will be gone. He is not coming here to the court,’ said Zeno.

Gallienus turned the fruit in his hand. It had a lustre in the spring sunshine. Biting into it, he took in the other men in the room. There were fourteen apart from himself: five civilians; heads of imperial chanceries, including Zeno; and nine military men. It was a small, intimate lunch after the formal consilium. The serious business of the morning was done. They had discussed at length the imperial decision, as implacable and irrevocable as that of a god, concerning the city of Byzantium.

‘Of course, Dominus, I am not suggesting a course of action.’ Zeno was losing confidence in the face of continued imperial silence. ‘It may well be he should be rewarded, rather than punished.’

Gallienus noted that, while all were quiet, only one of the others seemed especially interested. It was not Rufinus, the Princeps Peregrinorum. As head of the secret service, Rufinus should have been all ears. The man who was paying close attention, although hiding it well, was Censorinus, the deputy Praetorian Prefect.

It could be time for a change, thought Gallienus. Censorinus may be a low-bred individual, his misquotations of Homer the talk of the court, but he had served as Princeps Peregrinorum to both Gallienus’s father, Valerian, and the short-lived pretenders Macrianus and Quietus. He was a political survivor: untrustworthy, but ruthless and efficient. Gallienus knew he needed men with the latter qualities, and he had never been one to hold a man’s birth against him.

‘Try a pear,’ the emperor said to Zeno. ‘You know how I enjoy things out of season.’

A servant passed the silver fruit platter, and Zeno helped himself. Gallienus suppressed a smile. It may well be that Zeno detested pears, but an imperial suggestion always had the force of a command. And – the urge to smile was hard to resist – Zeno would be turning over all the possible meanings of what he had said, and must recognize the dangerous implications of ‘things out of season’.

‘My mind is not yet made up,’ Gallienus said. ‘But now I want my comites to advise me on my decennalia.’

Unsurprisingly, given the nature of the subject, it was a civilian, one of the heads of chanceries, who began. ‘ Dominus,’ said Caecilius Hermianus, the ab Admissionibus, ‘your ten glorious years on the throne demand a fitting, magnificent spectacle.’