As dusk settled over the port the cohort's commander peered down the cliff towards the river. A faint mist covered the Euphrates and spilled over the banks on either side, rising even above the trees that grew along the river, so that it seemed like the smooth belly of a snake, gently undulating across the landscape.The thought made the hairs rise on the back of Centurion Castor's neck. He pulled his cloak tightly about his chest, narrowed his eyes and stared towards the land spreading away on the far side of the Euphrates: Parthian territory.

It was over a hundred years since the might of Rome had first come into contact with the Parthians and, ever since, both empires had been playing a deadly game for control of Palmyra and the lands to the east of the Roman province of Syria. Now that Rome was negotiating a closer treaty with Palmyra her influence had spread to the banks of the Euphrates, right on the frontier with her old foe. There was no longer any buffer state between Rome and Parthia and few men had any doubt that the simmering hostility would flare up into a new conflict before long. The legions back in Syria had already been preparing for a campaign when the centurion and his men had marched out of the gates of Damascus.

The thought made Centurion Castor bitterly resent, once again, the orders he had received from Rome to lead a cohort of auxiliaries across the desert, far beyond even Palmyra, to establish a fort here on the cliffs above the Euphrates. Palmyra was eight days' march away to the west and the nearest Roman soldiers were based at Emesa, six days beyond Palmyra. Castor had never felt so isolated in his life. He, and his four hundred men, were at the very end of the Empire, posted on this cliff to watch for any sign of an attack by Parthia across the Euphrates.

After an exhausting march across the barren, rocky desert they had set up camp near the cliff and begun work on the fort they would garrison until some official back in Rome eventually decided to relieve them. During the march the cohort had baked under the sun during the day, and huddled in their cloaks each night as the temperature had dropped like a stone.Water had been strictly rationed, and when they had finally reached the great river that cut across the desert and watered the fertile crescent that lined the banks his men had rushed down into the shallows to slake their thirst, deliriously scooping water to their cracked lips, before their officers could restrain them.

Having served for three years in the Tenth Legion's garrison at Cyrrhus, with its fine well-watered gardens and all the pleasures of the flesh that a man could want, Castor regarded his temporary posting with growing dread. The cohort faced the prospect of spending months, perhaps years, in this far-flung corner of the world. If boredom didn't kill them first, then the Parthians surely would. That was why the centurion had driven his men to work on the fort as soon as they found a spot on this cliff that afforded fine views over the ford below, and the rolling plains of Parthia beyond. Castor knew that word of the Roman presence would swiftly reach the ears of the Parthian king and it was vital that the cohort threw up strong defences before the Parthians decided to take any action against them. For several days the auxiliaries had toiled to level the ground and prepare foundations for the walls and towers of the new fort. Then the masons had hurriedly dressed the slabs of rock that had been hauled by wagon from the surrounding outcrops on to the site. The retaining walls were already at waist height and the gap between them filled with rubble and spoil, and as he glanced over the site in the dying light Centurion Castor nodded with satisfaction. In five more days, the defences would have risen high enough for him to move the camp inside the walls of the new fort. Then they could afford to feel more secure from the Parthians. Until then the men would labour every hour that daylight allowed.

The sun had set a while ago and only a faint band of russet light still gleamed along the horizon. Castor turned to his second-in-command, Centurion Septimus. 'Time to finish for the day.'

Septimus nodded, drew a lungful of air and cupped a hand to his mouth as he bellowed the order across the construction site.

'Cohort! Down tools, and return to camp!'

Across the site Castor could see the dim shapes of men wearily stacking their picks, shovels and wicker baskets before taking up their shields and spears and shuffling into the lines forming outside the gap where the main gate would be. As the last of them moved into position the wind began to rise, out of the desert, and squinting towards the west Castor saw a dense mass rolling steadily towards them.

'Dust storm coming this way,' he grumbled to Septimus. 'Better get down to the camp before it hits.'

The other man nodded. Septimus had served on the eastern frontier for most of his career and well knew how quickly men could lose their sense of direction once they were engulfed in the choking, abrasive sand whipped up by the winds that swept these lands.

'Those lucky bastards down in the camp are well out of it.'

Castor smiled briefly. A half-century had been left to guard the camp while their comrades toiled away up on the cliff. He could imagine them already retreating into the shelter of the sentry turrets, out of biting wind and sand. 'Well then, let's get the men moving.'

He gave the order to advance and the men trudged forward, down the winding track that led to the camp, just over a mile from the site of the fort.The wind picked up as the gloom thickened over the landscape and the soldiers' capes fluttered and whipped about them as they descended the rock-strewn route from the cliff.

'Shan't be sorry to leave this place, sir,' Septimus growled. 'Any idea how long before we're replaced? There's a warm billet waiting for me and the lads at Emesa.'

Castor shook his head. 'No idea. I'm as keen to get out of here as you are. All depends on the situation in Palmyra, and what our Parthian friends decide to do about it.'

'Fucking Parthians,' Septimus spat. 'Bastards are always stirring it up. It was them that was behind that business down in Judaea last year, wasn't it?'

Castor nodded as he recalled the uprising that had flared up east of the Jordan river. The Parthians had supplied the rebels with arms and a small force of horse-archers. It was only thanks to the gallant efforts of the garrison at Fort Bushir that the rebels and their Parthian allies had been prevented from inciting the whole of Judaea to rise up against Rome. Now, the Parthians had turned their attention to the oasis city of Palmyra – a vital link in the trade routes to the east and a buffer between the Roman Empire and Parthia. Palmyra enjoyed considerable independence and was more of a protectorate than a subject state. But the king of Palmyra was growing old and the rival members of his household were jockeying for position to become his successor. One of the most powerful of the Palmyran princes had made little secret of his desire to throw in his lot with Parthia, if he became the new ruler.

Castor cleared his throat. 'It's down to the governor of Syria to convince the Parthians to keep their hands off Palmyra.'

Centurion Septimus cocked an eyebrow. 'Cassius Longinus? Think he's up to it?'

Castor was silent for a moment as he considered his reply. 'Longinus can handle it. He's no imperial lackey; he's earned his promotions. If he can't win the diplomatic battle then I'm sure he'll take them apart in a fight. If it comes to that.'

'Wish I shared your confidence, sir.' Septimus shook his head. 'From what I heard, Longinus took to his heels pretty quickly last time he was in trouble.'