'Who told you that?' Castor snapped.

'I got it from some officer in the garrison at Bushir, sir. Seems that Longinus was at the fort when the rebels turned up.The governor was in his saddle and out of there quicker than a Subura whore goes through your purse.'

Castor shrugged. 'I'm sure he had his reasons.'

'I'm sure he did.'

Castor turned to his subordinate with a frown. 'Look, we've no business debating the governor's finer points. Especially not in earshot of the men. So keep it to yourself, understand?'

Centurion Septimus pursed his lips for a moment and then nodded. 'As you wish, sir.'

The column continued down the slope, and as the wind strengthened the first swirl of dust swept across the track. Within moments all sign of the surrounding landscape had vanished and Castor slowed his pace to make certain that he was still leading his men along the track to the camp. They edged forward, shoulders hunched as they did their best to shelter behind their shields from the blasts of sand. At length the track levelled out as they reached the foot of the slope. Even though the fort was only a short distance ahead, the sand and gathering darkness hid it from view.

'Not far now,' Castor muttered to himself.

Septimus overheard him. 'Good. First thing I do when I reach my tent is clear my throat with a drop of wine.'

'Good idea. Mind if I join you?'

Septimus gritted his teeth at the unexpected request, and moodily resigned himself to sharing the last flask of the wine he had brought across the desert from Palmyra. He cleared his throat and nodded. 'It'd be a pleasure, sir.'

Castor laughed and slapped him on the shoulder. 'Good man! When we get back to Palmyra, the first drink's on me.'

'Yes, sir. Thank-' Septimus suddenly drew up sharply and strained his eyes along the track ahead of them.Then he thrust up his hand to signal the column to halt.

'What's the matter?' Castor said quietly as he stood close to the side of his subordinate. 'What is it?'

Septimus nodded towards the fort. 'I saw something, just ahead of us. A horseman.'

Both officers stared into the swirling sand before them, straining their ears and eyes, but there was no sign of anyone, mounted or on foot. Just the smudges of stunted shrubs that grew either side of the track. Castor swallowed, and forced his tensed muscles to relax.

'What exactly did you see?'

Septimus glanced at him with an angry expression, sensing his superior's doubt. 'As I said, a horseman. About fifty paces ahead. The sand cleared for a moment and I saw him, just for an instant.'

Castor nodded. 'Sure it wasn't just a trick of the light? Could easily have been one of those bushes moving.'

'I'm telling you, sir. It was a horse. Plain as anything. I swear it by all the gods. Up there ahead of us.'

Castor was about to reply when both men heard a faint metallic ringing above the moan of the wind. The sound was unmistakable to any soldier: the clash of sword against sword. An instant later there was a muffled shout, and then nothing apart from the wind. Castor felt his blood chill in his veins as he turned to Septimus and spoke quietly.

'Pass the word to the other officers. Have the men formed up in close order across the track. Do it quietly.'

'Yes, sir.' Centurion Septimus saluted and dropped back to pass the word down the line. While the men fanned out on either side of the track Castor took a few strides closer to the camp. A freak shift in the wind gave him a faint glimpse of the gatehouse and a body slumped against the timber frame, which was studded with several arrows. Then a veil of dust hid the camp from view again. Castor backed away towards his men. The auxiliaries stood in a line four deep across the track, shields held high and spears angled forward as they gazed anxiously towards the camp. Septimus was waiting for his commander at the head of the century on the right flank. Beside them the slope rose up into a tangle of rocks and undergrowth.

'Did you see anything, sir?'

Castor nodded and waited until he stood beside the other officer before he spoke in a low voice. 'The camp's been attacked.'

'Attacked?' Septimus raised his eyebrows.'Who is it? The Parthians?'

'Who else?'

Septimus nodded and his hand slid down and grasped the handle of his sword. 'What are your orders, sir?'

'They're still close. In this sandstorm they could be anywhere. We have to try to get back inside the camp, clear them out and get the gate closed. That's our best chance.'

Septimus smiled grimly.'Our only chance, you mean, sir.'

Castor did not reply, but flicked the folds of his cape back over his shoulders and drew his sword. He raised it high and glanced along the line to make sure that the other officers were following his example and passing the signal on. Castor had no idea how many enemies they faced. If they were bold enough to storm and take the camp, then they must have attacked in some strength. The mist over the river and the rising sandstorm would have covered their approach. Castor drew small comfort from the fact that the same sandstorm would now provide some cover for the rest of the cohort as they approached the fort.With luck, the auxiliaries might even surprise the enemy in turn. He slowly lowered his sword arm, the tip arcing down towards the fort. The signal was repeated down the line and on to those men to his left who were hidden in the gloom and dust.

Castor drew his sword in until the side of the blade rested against the rim of his shield and then he stepped forward. The line rippled after him as the auxiliaries trod steadily over the broken ground towards the camp. The officers kept the pace slow enough to be able to dress the line as it advanced. To the right the slope gave way to open ground as the flanking century moved away from the cliff. Castor stared ahead with narrowed eyes, looking for any sign of the enemy, or the fortifications of the camp.Then he saw it, the bulk of the main gate emerging from the sweep of dust and sand. The outline of the raised palisade on either side resolved itself into sharp detail as the auxiliaries closed on the camp. Apart from the body resting against the gate post there was no sign of anyone else, living or dead.

The sound of hooves thrummed across the ground to his right and Castor turned to look just as one of his men on the end of the line cried out and snatched at the shaft of an arrow that had pierced his chest. Dim shapes burst through the veil of the sandstorm as several Parthian horse-archers galloped up to the auxiliaries and loosed their arrows into the unprotected right sides of the Roman soldiers. Four more men were hit and tumbled to the ground while another doubled over, but tried to stay on his feet as he wrestled with an arrow that had passed through his thigh and pinned it to the other leg. The Parthians wheeled their mounts to one side and raced back out of sight, leaving the auxiliaries staring after them in surprise and terror.

Almost at once there was a cry from the left as the enemy made another attack.

'Keep moving!' Castor cried out in desperation as he heard yet more horses passing behind the cohort. 'Run, boys!'

The ordered lines of the cohort dissolved into a mass of men running towards the main gate, Castor amongst them. Then he saw the gates closing and at once scores of faces appeared above the palisade. Bows were raised and again the sound of arrows hissed through the air and more of the auxiliaries were struck down as they drew up helplessly in front of the camp.There was no let-up in the rain of arrows that clattered off shields, or pierced flesh with a wet thud. Voices were crying out on all sides and with a sick feeling in the pit of his stomach Castor realised that his men were as good as dead, unless he did something.

'On me!' Castor roared out. 'Close up on me!'