Ballista looked around through the thick, jaundiced air. There were no buildings, and it was flat here, all the way down to the harbour. ‘After a shock, there can be a tidal wave.’

Hippothous nodded, an oddly calm and judicious nod, as if he were discussing a proposition in a philosophical school. ‘Not always, and we are hundreds of yards from the sea. There is only a tidal wave if there is an onshore wind opposing the escaping air. The sky is calm today.’

Ballista did not reply at once. He looked at the crowds standing vacant, occasional eddies of imbecilic motion in the murk – all irrational, possibly dangerous. He could not leave his sons here. He would not be parted from them now.

‘We will all go,’ Ballista said.

The Gate of Mazaeus and Mithridates loomed out of the gloom. On its top, some statues still stood. Ballista eyed them suspiciously. The square beyond the gate was a deserted shambles. To the right, tendrils of smoke issued from the facade of the library of Celsus. Ahead, the big Parthian war monument had collapsed; the barbarians and their conquerors, both indiscriminately hurled to the ground. Ballista quickly led the group away to the left. He hoped the boys had not noticed the fallen statue and the crushed body of Anthia.

Emerging into the Sacred Way, they saw the scale of the destruction and its inhuman randomness. Some buildings stood pristine; next to them, a whole block had imploded. The temple of Hadrian and the Varius Baths appeared untouched. The block opposite, the insula of their rented house, had given way.

‘Gods below…’

The street itself was partly blocked. Clambering over the debris, they reached the foot of the slope where the rented house had stood.

Ballista took stock. There were people here, many rooted in shock, but others moving more purposefully. Scurrying like ants over the ruins – rescuers or looters, you could not tell. The familia closed up around Ballista. They were waiting, except Julia, who continued blank-eyed with shock. Why could someone else not take the decisions? Ballista pushed aside the childish thought.

‘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.