‘Isangrim, stay with your mother.’ Ballista turned to the remaining maid. ‘Rhode, take good care of Dernhelm; stay close to your domina. Hippothous, guard the women and children. Keep out of the lee of the buildings, try to stay in the middle of the street.’

Ballista grinned resignedly at Maximus and Calgacus. ‘We had better do what we can.’ He gestured at their bedraggled togas. ‘These will not help. We should leave them here.’

As the three men began to strip down to their tunics, Ballista realized that, somehow, the mural crown was still on his head. He passed it to Hippothous. ‘Look after it. I lost one once in Antioch; cost a fortune to replace.’ The bloodshot eyes of the accensus gleamed. Ballista wondered if he was one of those men with a passion for gold. Certainly, he had been little better than a bandit back in Cilicia.

‘We should take the togas,’ said Calgacus. ‘They can be tied into ropes.’

‘Allfather, you are right.’ Ballista shook his head. ‘We have nothing, not even a weapon between us.’

His freedmen both smiled. From somewhere or other, Maximus produced a serious knife. Calgacus had two. The old Caledonian handed one to Ballista, who gave it over to Hippothous.

‘You really are nasty, dangerous bastards.’ Ballista laughed.

‘Sure, and you have always been too trusting,’ replied Maximus.

The three men gave their attention to the slope. The path between the two blocks of houses was gone. Walls had toppled sideways to bury it. But most of the buildings had collapsed forwards, sliding down the hillside. They would have to climb over the fallen roofs, the exposed beams and masonry.

The material of his toga knotted over his shoulder, Ballista set off. They climbed spread out, careful not to get in front of each other. The ruins were hideously unstable. If one of them caused a slip, anyone behind him was liable to be crushed as well. It was painfully slow going. Every hand and foothold threatened injury; jagged tiles and exposed nails were everywhere.

Allfather, this is near-suicide, thought Ballista. The whole lot could go at any moment, even without the terrible likelihood of an aftershock. Out of nowhere came the realization that he was clambering over the dead and dying – even worse, over the uninjured and trapped. He inched upward.

The house, when they eventually reached it, was just recognizable: a weirdly truncated version of what it had been. It had shifted forward, and the floors had collapsed down on top of each other. The headroom of each chamber had been reduced to no more than a couple of feet. The beams of the ceilings stuck out in rows just above each other. It did not look as if it had ever been a real house. It reminded Ballista of one of those fancy Italian cakes built in layers.

They got on top of it, tore away tiles, called down into the rubble. They listened. Nothing came back from the house; just distant shouts and screams, and far too close squeals and sharp cracks as timber and masonry settled or fell. There was a half-scented smell of woodsmoke.

There was a dip where the atrium had been. Digging down from the top of the house was hopeless. With few words, they crept towards the hollow. Maybe they could tunnel in from the side.

A deep menacing roar rose from below. They stopped, gazed down. A breeze had got up, was blowing away some of the Stygian gloom. A lone figure was haring up the Sacred Way. He ran heedless, scrambling over obstructions, pausing for nothing. At no great distance behind him came the pursuit, a throng spilling out from the agora, past the smouldering library of Celsus. The mob was baying for blood – the worst sound in the world.

The man was heading straight for Julia and the boys. Paralysed with impotence, Ballista watched. Allfather, Deep Hood, Death-blinder, let them be safe.

Hippothous had seen the man coming. He was herding the familia back behind the columns of the facade of the small temple of Hadrian. The man tried to dive in after them. Hippothous stepped out from the central arch. His arm moved; sunlight glinted on the blade. The man sheered off, ran on. He looked tired, not moving well.

The mob was gaining. They surged past the temple of Hadrian. They were yelling, giving voice to their hatred. Snatches floated up to Ballista: Kill the arsonist, the atheist… Christians to the lion.

The man broke stride by the turning into the path up to the governor’s palace. Deciding against it, he ran on up the Embolos.

He only got as far as the Fountain of Trajan before they were on him. A hurled stone brought him down. He tried to get to his feet. Someone kicked him down again. He disappeared: the centre of surging, kicking frenzy.

‘Gods below!’ said Maximus. ‘See the women.’

Ballista saw it was worse than the Hibernian had said; there were even children in the lynch mob. He looked away down the street. Hippothous was doing well. He was keeping the familia back in the temple of Hadrian, sparing the boys the sickening sight.

The crowd parted momentarily. The man was on his feet again. They were clawing at him, beating him, pulling him this way and that. He was not young. Now he was bloodied, beyond pleading.

‘Poor bastard,’ said Maximus.

The man went down once more. The mob closed in, like hounds breaking up a beast.

‘Poor bastard,’ said Maximus again. Poseidon, Earth-holder, steadfast stabilizer; Avert your anger, Hold your hands over us Phoebus Apollo…

The celebrants of this impulsive blood rite held their stained hands to the sky. Their hymn drifted up; to the three men watching on the slope, above to the Olympian gods. Presumably, the deities on high would be pleased – if they existed.

Down on the Embolos, the knot of humanity began to unravel. Men, women and children drifted away. At a distance, they started to look more deflated than exalted.

In the misty spring sunshine the body lay abandoned in the middle of the Sacred Way.

Up on the slope, the three men did not speak of it. There was nothing to say. With no words at all, they resumed their delicate traverse to the hollow of the atrium.

Before he shifted over the edge, Ballista looked down on the Embolos. He was pleased Hippothous had got the familia out of the temple of Hadrian. Ballista did not trust its slender columns to withstand another shock. The corpse lay in the street not far from them, but that could not be helped. It was the manner of the slaying he had wished his sons not to see, not its happening or its aftermath. After all, what child had not witnessed violent death, in the arena or elsewhere, had not seen the bodies on the crosses outside virtually every town in the imperium?

The sides of the depression were seamed with jagged rents like badly cut niches in a tomb. Some of the openings were no bigger than a baby; others could admit a man. They clambered perilously, peering into the dark, dust-choked holes, calling, listening for signs of life.

‘Here.’ Maximus summoned the other two. Muffled sounds; crying – an infant?; a woman’s voice – Help, somebody help.

‘I will go,’ said Maximus. ‘All the good living has left you two as fat as gladiators.’

Ballista felt a surge of gratitude. Maximus was one of the very few who knew his fear of confined spaces.

They cut and rolled one of the togas into a rope, tied it around Maximus’s waist, spliced another to it.

‘Three sharp tugs, and we want you out of there,’ said Ballista. ‘You do the same, and we will start pulling you out.’

Maximus nodded. With no discernible hesitation, he levered himself into the hole.

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.