'If we don't trust Balthus, we should send one of our men in with his courier. Just to make sure he doesn't go astray, and that the citadel's defenders are ready for us.'

Macro considered the suggestion for a moment and then looked at Cato with a sad, weary expression. 'I know what you're going to say. I know it before you even open your mouth.You're not going.Your men need you. Frankly, I need you. There's going to be action tonight, and I would feel easier about it if I knew the Second Illyrian was safe in your hands.'

Cato stared at his friend for a moment and his heart filled with affection for the gruff, honest man who had taught him how to be a soldier, and how to be a leader of men. Macro was Cato's ideal. He was the true measure of a soldier in Cato's eyes, and the thought that Macro depended on him was an accolade far beyond praise from the veteran. Cato bit back on his pride and affection.

'Centurion Parmenion can lead the men as well as me.'

'No.' Macro shook his head and then grinned. 'He can do it better. I just don't like to be shown up. Far better to have you to compete against.'

They laughed, and then Cato continued,'I have to go.To make sure that everything is ready from the other end. If we're going to be betrayed, better to lose me than both cohorts.'

'How will I know if it's safe to go through with Balthus' plan?'

'I've thought of that. If I make it through to the citadel then I'll have them light a beacon in the highest tower.You and Balthus rush the gate the moment you see it. If there's no signal by first light, then you'll have to accept that I've failed. Is that all right, sir?' The deferential tone was deliberate. Cato knew that the final decision was Macro's alone and if he refused then there was no further debating the matter.

Macro rubbed the bristles on his cheek. 'Very well. Give Parmenion his orders and then report to me. I'll be with our friend the prince, deciding on our message to the king.'

By the time Cato rejoined Macro the sun was low on the horizon and the evening shadows were creeping across the plain. One of Balthus' men was standing with his prince and Macro, holding some dark robes over his arm.

'This is Carpex, one of my household slaves,' Balthus explained. 'He is as loyal a man as you can find.'

'For a slave,' said Macro.

'Yes. But I would trust him with my life,' Balthus said.

'That's good. Because that's exactly what we are trusting him with.Yours, and ours.'

Carpex gestured to the robes as he addressed Cato. 'You'll need to wear these, master. Better leave your armour and keep your weapons covered.The rest of your equipment has to be left behind.'

'How are we going to get through to the citadel?' Cato asked.

'There is a way,' said Balthus. 'A tunnel leading from one of the city's drains into the old stables of the citadel. They use the building as a barracks now, but Carpex and I discovered it when we were boys, and used to hide there to escape punishment.'

'How mischievous of you,' said Macro. 'And when did you last use this tunnel?'

'Ten years ago.' Balthus pursed his lips. 'Maybe more.'

'I see. So there's no guarantee it hasn't been blocked up, or filled in, then?'

'It's still there as far as I know.'

'And if it isn't?' asked Cato.

'Then we will have to try some other way.'

'Fair enough.' Cato nodded.'We'll have to deal with that problem if it arises.'

Macro shook his head. 'That's madness.'

'Perhaps,' Cato admitted. 'But sometimes madness is all that's left.'

'Oh, how very sage.'

Cato shrugged and turned to the prince's slave. 'Where's the message?'

Balthus pulled a waxed slate from his robes and handed it to Cato. 'Here.'

'Is it, er, sufficiently clear?' Cato asked Macro.

His friend smiled. 'It says all that it needs to. No surprises.'

'Good,' Cato replied and tucked the waxed tablet into his haversack. Then he removed his helmet, cape, harness and armour and handed them to Macro, before leaning down to remove his silvered greaves. By the time he had put on the robes and fastened the band round his headdress he no longer looked so Roman, and he hoped that he would pass as a Palmyran subject – in the dark at least. As the sun eased itself down towards the horizon, Cato and Macro sat a short distance up the slope from the rest of the men. Almost as soon as he had propped himself up against a boulder, Macro fell asleep. His head lolled on his chest and he began to snore. Cato could not help smiling. Tired as his body was he could never sleep on the eve of any action, and his mind raced through seemingly disparate trains of thought. Now that the first thrill at the prospect of danger was over, Cato found that he was trembling and was aware that his knee was twitching in a frantic rhythm. He stared at it in surprise and had to force himself to stop the nervous tic.

Then, for no accountable reason, the image of the man he had wounded flashed into his mind. He could see every detail of the fearful surprise in Primus' expression as the blade lodged deep in his shoulder. Primus had slipped into unconsciousness and died the day before, and was buried back in the desert under a pile of rocks to stop wild animals digging up his body. Cato had not seen him since the night of the fight, yet he was haunted by the image of the man he had wounded. At length he could bear it no longer and he nudged Macro.

'Hey, wake up.'

'Hmmm?' Macro mumbled, smacking his lips and turning slightly away from Cato. 'Fuck off, I'm asleep.'

'No you're not. Come on, wake up. I need to talk. Sir?' Cato shook his shoulder gently.

Macro stirred, blinked and eased himself up from the rock, wincing at the stiffness in his back. 'What? What is it, Cato?'

Now that he had his friend's attention Cato was not sure where to begin. He swallowed nervously. 'Something happened the other night. When we ambushed the horse-archers. Something I haven't told you about.'

'Oh? Well, what is it?'

Cato breathed deeply and made himself confess. 'During the fight, I…I wounded one of my men. Ran him through with my sword.'

Macro stared at him for a moment, then rubbed his eyes. 'You did what?'

'I wounded one of my auxiliaries.'

'Is he dead?'

'Yes.'

'Did he recognise you?'

'Yes.' Cato recalled the man's accusing look, and shook off the memory with difficulty. 'I'm sure of it.'

'Did he tell anyone about it?'

'I don't know.'

'Hmmm. Awkward. Normally it would just be one of those things. Accidents happen in the heat of battle, especially at night. But it still needs to be accounted for. It won't look good on your record if there's any kind of enquiry. Even if there isn't, word will get round, assuming the man spoke to anyone. You know how it is with the army's rumour mill. That's not going to go down well with your men. Nor mine, come to that. Not while the memory of that incident back at Antioch preys on their minds.'

'But it was an accident,' Cato protested. 'It was dark. It was during a fight. I didn't mean to do it.'

'I know that, lad. Trouble is that the boys in the Tenth Legion won't see it that way. They'll say that Crispus killed his man by accident and was executed for it.They're bound to ask why you shouldn't suffer the same fate. I know the circumstances are quite different, but that's the kind of detail that men ignore when they nurse a grievance and are out for revenge.'

Cato was silent for a moment before he looked earnestly at his friend. 'What can I do?'

'Not much. If Primus died without spilling his guts then you're in the clear.' Macro paused, and smiled. 'Well, hardly that. Knowing you as I do, you'll carry the burden of guilt with you to the grave. If Primus talked, then you'll be treated like a leper. Worse, you'll have to watch your back.'