‘You think I give a shit about how this bastard died?’ Gallo snorted dismissively. ‘Don’t forget who he was or who he worked for. All I want to know is who killed him, why they did it here and why like this. The last thing I need is some sort of vigilante stalking the streets of Rome re-enacting Satanic rituals.’

‘Actually, Colonel, it’s Christian, not Satanic,’ Allegra interrupted with a cough.

‘What?’ Gallo rounded on her, looking her up and down with a disdainful expression. He was six feet tall and powerfully built, with a strong, tanned face covered in carefully trimmed stubble. About forty-five or so, she guessed, he was wearing the full dress uniform of a colonel in the Guarda di Finanza and had chin-length steel-grey hair that parted down the centre of his head and fell either side of his face, forcing him to sweep it back out of his eyes every so often. He also had on a pair of frameless glasses with clear plastic arms. From the way he adjusted them on his nose, she sensed that these had only recently been prescribed and that he still resented wearing them, despite having done what he could to make them as unobtrusive as possible.

‘The inverted crucifixion,’ she explained, ignoring the horrified look on Salvatore’s face. ‘It’s taken from the Acts of Peter.’

‘The Acts of Peter?’ Gallo snorted. ‘There’s no such book in the Bible.’

‘That’s because it’s in the Apocrypha, the texts excluded from the Bible by the church,’ she replied, holding her temper in check. ‘According to the text, when the Roman authorities sentenced Peter to death, he asked to be crucified head down, so as not to imitate Christ’s passing.’

Gallo said nothing, his eyes narrowing slightly as he brushed his hair back.

‘Thank you for the Sunday school lesson, Miss…’

‘Lieutenant. Damico.’

‘The antiquities expert you asked for, Colonel,’ Salvatore added quickly.

‘You work at the university?’ It sounded like a challenge rather than a question.

‘I used to be a lecturer in art and antiquities at La Sapienza, yes.’

‘Used to be!’ he spluttered, glaring at Salvatore.

‘The university passed me on to the Villa Giulia. One of the experts there recommended her,’ Salvatore insisted.

‘Now I’m in the TPA,’ she added quickly, spelling out the acronym for the Nucleo Tutela Patrimonio Artistico, the special corps within the Carabinieri tasked with protecting and recovering stolen art. He looked her up and down again, then shrugged.

‘Well, you’ll have to do, I suppose,’ he said, to Salvatore’s visible relief. ‘I take it you know who I am?’

She nodded, although part of her was itching to say no, just to see the look on his face. Ignoring the other two men standing there, which she assumed meant that he did not consider them important enough to warrant an introduction, Gallo jabbed his finger at the man next to him.

‘This is Dottore Giovanni la Fabro from the coroner’s office, and this is, or was, Adriano Ricci, an enforcer for the De Luca family.’

Allegra nodded. The GICO’s involvement was suddenly a lot clearer. The De Luca family were believed to run the Bande della Magliana, one of Rome’s most notorious criminal organisations. Gallo clearly thought this was some sort of professional hit.

He stepped back and introduced the corpse with a sweep of his hand. Even dead, she could tell that Ricci had been overweight, loose skin sagging towards the ground like melted wax on the neck of a bottle. He was bare-chested with a large Lazio football club tattoo on his left shoulder, and was still wearing a striped pair of suit trousers that had fallen halfway down his calves. His wrists and ankles were bleeding where the chicken wire used to bind him to the cross had bitten into his flesh.

‘Why am I here?’ she asked with a shudder, glancing back to Gallo.

‘This -’ He led her forward to the body and snapped his flashlight on to illuminate its face.

For a few moments she couldn’t make out what he was pointing to, her attention grabbed by Ricci’s staring, bloodshot eyes and the way that, from the shoulders up, his skin had turned a waxy purple, like marble. But then, trapped in the light of Gallo’s torch, she saw it. A black shape, a disc of some sort, lurking in the roof of Ricci’s mouth.

‘What is it?’ she breathed.

‘That’s what you’re meant to be telling me,’ Gallo shot back.

‘Can I see it, then?’

Gallo snapped his fingers and la Fabro handed him a pair of tweezers. To Allegra’s horrified fascination, he levered the object free as if he was prising a jewel from an ancient Indian statue and then carefully deposited it inside an evidence bag, holding it out between his fingertips as if it contained something mildly repellent.

‘Knock yourself out,’ he intoned.

‘I thought it might be some sort of antique coin,’ Salvatore suggested eagerly over her shoulder as she turned it over in the light. ‘It seems to have markings etched into it.’

‘The ancient Romans used to put a bronze coin in the mouths of their dead to pay Charon to ferry their souls across the Styx to the Underworld,’ she nodded slowly. ‘But I don’t think that’s what this is.’

‘Why not?’

‘Feel the weight, it’s lead. That’s too soft to be used in everyday coinage.’

‘Then what about the engraving?’ Gallo asked impatiently.

She traced the symbol that had been inlaid into the coin with her finger. It showed two snakes intertwined around a clenched fist, like the seal from some mediaeval coat of arms.

‘I don’t know,’ she said with an apologetic shrug. ‘But whatever this is, it’s not an antique nor, I would say, particularly valuable.’

‘Well, that was useful.’ Glaring angrily at Salvatore, Gallo turned his back on Allegra as if she had suddenly vanished.

‘I’m sorry,’ Salvatore stuttered. ‘I thought that…’

‘We’ve wasted enough time. Let’s just get him bagged up and out of here so the forensic boys can move in,’ Gallo ordered as he turned to leave. ‘Then I want a priest or a cardinal or somebody else in sandals down here to tell me more about…’

‘It can’t be a coincidence though, can it, Colonel?’ Allegra called after him.

Gallo spun round angrily.

‘I thought you’d gone?’

‘It can’t be a coincidence that they killed him here?’ she insisted.

‘What the hell are you talking about?’

‘In Roman times, this entire area was part of the Campus Martius, a huge complex of buildings that included the Baths of Agrippa to the north, the Circus Flaminius to the south and the Theatre of Pompey to the west,’ she explained, pointing towards each point of the compass in turn. ‘The Senate even met here while the Curia was being rebuilt after a fire in 54 BC -’ she pointed at the floor – ‘in a space in the portico attached to the Theatre of Pompey.’

‘Here?’ Gallo looked around him sceptically, clearly struggling to reconcile the fractured ruins at his feet with the imagined grandeur of a Roman theatre.

‘Of course, the one drawback of this spot was that the Campus Martius stood outside the sacred pomerium, the city’s official boundaries, meaning that, although it was quieter than the Forum, it was not subject to the same restrictions against concealed weapons.’

‘What’s your point?’ Gallo frowned wearily, and she realised that she was going to have to spell it out for him.

‘I mean that Ricci isn’t the first person to be killed here,’ she explained, a tremor of excitement in her voice. ‘I mean that in 44 BC, Julius Caesar was assassinated on almost this exact same spot.’