'It must be a parade,' said Petronius scornfully. 'Mithridates wants to tell his soldiers how brave they are.'

'Maybe he wants Caesar to deploy more men out here,' Romulus countered.

Petronius frowned. 'To slow down the construction of the fortifications?'

Romulus inclined his head. If their entire force constantly had to defend their camp, it would never get built.

'He's probably just showing off his army. Boosting their confidence. It is much bigger than ours, after all,' muttered Petronius.

This was quite plausible. Romulus grinned, glad of the Roman legionary's psychological advantage over other troops.

The pair glanced at their camp, wondering how their general would respond. It was not long before a red-cloaked figure had climbed on to the ramparts, followed by a group of senior officers and a single trumpeter. A loud cheer rose up at the sight of Caesar, who was deliberately making himself visible while getting a better view of the enemy. Lifting a hand to shield his eyes, Caesar peered into the distance. He studied Mithridates' host for a long time.

Romulus did likewise. At the very front he could make out groups of slingers and archers, the missile troops which led most attacks, their purpose to cause as many casualties as possible. Behind them, the war chariots formed up in the centre, with thousands of peltasts and thureophoroi arrayed in a tight square close behind. On the left wing sat the Pontic heavy cavalry, while on the other an unruly mass of lightly armed Thracian horsemen assembled.

'That looks like battle order to me,' Romulus muttered.

'It does,' agreed the other with a suspicious growl. 'Here comes Mithridates now.'

Rapt, they watched a rider on a magnificent black stallion emerge from the camp gates to rousing cheers from the waiting host. He was followed by a number of mailed warriors on similar steeds. Crying out in a deep voice, Mithridates moved slowly across the front of the host. Loud, admiring shouts rang out in response and the distinctive sound of swords being hammered off shields mixed with that of clashing cymbals and pounding drums. Like those in any army, the Pontic soldiers revelled in the attention of their master. Reaching the centre, Mithridates spent a long time enjoining the charioteers, and Romulus' unease grew. By the time the king had addressed his entire force, the noise levels on the other side of the valley had grown to a threatening crescendo.

'Let them shout,' said Petronius contemptuously. 'It makes no odds to us.'

Perturbed, Romulus took a look at Caesar, whose stance had not changed. Nothing seems to panic this general, he thought with relief.

Caesar turned to confer with his officers. After a few moments, he faced the Twenty-Eighth, every man of which was watching him intently. 'They're just showing off, comrades,' he declared confidently. 'It's nothing to worry about. There'll be no battle today. Finishing our fortifications is far more important.' At his words, an audible sigh of relief went up. Satisfied, Caesar clambered down to the intervallum and disappeared.

'As you were,' shouted the officers. 'Back to work.'

Once again, pickaxes and shovels rose and fell. Carrying rocks for the ballistae, the braying mules were urged forward towards the walls. A surveyor emerged from the front gate, talking with a colleague. Behind him scuttled a slave clutching the groma, the device that helped his master to lay out a rectangular grid of the camp every day. A pair of straight, crossed sticks on a vertical pole, the groma had a lead weight dangling from the end of each of its four arms.

Relaxing, Petronius and the rest of Romulus' comrades began chatting among themselves. Once again, their job was the easiest on offer. The optiones and centurions did little to stop the idle banter. If Caesar was unconcerned, so were they.

Romulus' study of the enemy did not let up, however. Mithridates continued talking, and at last a long, rousing cheer went up from his assembled troops. Romulus cursed.

'Caesar got it wrong,' he blurted. 'The bastards are going to attack.'

Petronius gave him an incredulous glance, but this changed as he too studied the Pontic host. Other men began to notice as well.

Mithridates had already moved to one side, allowing the slingers and archers to lope down the slope first. Next came the scythed chariots, their axles creaking loudly. Alongside those trotted the heavy cavalry and the Thracian horsemen, forming a second wave of men and steeds. Taking up the rear were the peltasts and other infantry. Romulus' main concern, though, was the Pontic chariots and the massive amount of mounted support they had on each wing. If Mithridates' army was making the crazy decision to attack uphill, he and his comrades would struggle to hold back an all-out attack. Most of Deiotarus' riders were absent still.

Soon the roiling mass of chariots and horsemen had reached the bottom of the opposite slope. There was a pregnant pause and, in the lines of the Twenty-Eighth, everyone held their breath. Would the enemy move off along the valley floor, or make the fateful decision to charge upwards, towards their lines?

Romulus was glad to see that their optio was now observing too, but neither he nor any of the centurions seemed alarmed yet. It wasn't that surprising, he supposed. Attacking up a hill was most unwise. Romulus scowled, worried that this was more than just an enemy manoeuvre. There was no harm being prepared, in warning Caesar. Was the officers' belief in him so strong that they couldn't see what was happening right before their eyes?

The lead slingers and archers leapt into the water, quickly followed by their comrades. Holding their bows and slings high, they soon waded across, looking up at the Roman position. Horses whinnied as they were forced into the stream, yet the heavy cavalry maintained good order while crossing. Typical of irregular troops, the Thracians traversed in a disorganised mob, shouting and laughing. Loud rumbling noises and splashes ascended from the chariots, which were also being driven into the calf-high water without hesitation. On an area of flattish ground, the Pontic soldiers reassembled, quickly reassuming their original positions. All were now glancing upwards, while their officers pointed and shouted commands.

'They couldn't be that stupid,' breathed Petronius.

'I wouldn't be so sure,' replied Romulus grimly.

There was a short delay as the last enemy warriors urged their mounts into line. Then, started by the lead charioteers, an angry shout left their throats and, as one, they began to move forwards. Uphill.

'Jupiter!' Petronius exclaimed. 'They're mad.'

Their centurion finally acted. 'We're under attack!' he shouted. 'Sound the alarm!'

Raising his instrument to his lips, the nearest trumpeter blew a short, sharp series of notes over and over again. The response of the Twenty-Eighth was fast, the officers ushering the cohorts into close order while reducing the gap with its neighbour on each side. Deiotarus' horsemen – scarcely a hundred strong – moved together uneasily. Then the legionaries working on the ditches and ramparts took in the closely packed ranks climbing the slope. Led by their officers, they charged on to the intervallum and ran for their shields and pila.

It was slow, thought Romulus. Far too slow.

The protection they needed – the remainder of Deiotarus' cavalry – was nowhere to be seen. Furthermore, it would take the legions in the camp half an hour to find all their kit, assemble and march out to do battle. By that time the Twenty-Eighth would have been annihilated. Looking around, Romulus could see the same shocked realisation appearing on men's faces. Yet they had to stay put: without their protection, their ill-prepared comrades inside the walls would suffer the same fate.