The troops had suffered crossing the Alps before the spring sunshine had melted the snows in the passes. They had expected to be welcomed as liberators. They had been told that they only need set foot in Italy for everyone to come running, holding out olive branches, pushing forward their children, begging for mercy, falling at their feet.

It had not happened as they had hoped. They had come down from the mountains into an empty landscape. The inhabitants had fled, taking with them everything that they could move. Even the doors of their houses and temples were gone. The normally bustling plains were deserted. As the soldiers passed through the city of Emona the only living thing they found was a pack of wolves.

Now the army had been camped for over a month outside the walls of the north Italian city of Aquileia. The legions and auxiliaries were hungry, thirsty and tired. The hastily improvised supply chain had broken down. There was nothing to be had locally. What the citizens had not gathered within the walls, the soldiers themselves had wasted when they first arrived. There was no shelter. All the buildings in the suburbs had been torn down to provide materials for siege works. The river was polluted with the corpses of both sides.

The siege was making no progress. The walls could not be breached; there were not enough siege engines, the defenders were too effective. Each attempt to storm the walls with siege ladders and mobile towers ended in bloody failure.

Yet you could not fault the big man’s courage. Every day the Emperor Maximinus Thrax would ride around the town, well within bowshot range of the enemy, calling out encouragement to his men in the siege lines. As he passed through the ranks he promised them the town and everyone in it to do with as they pleased. While his courage had never been in doubt, his judgement had always been suspect. Now with every new reverse he became more savage. Like a wounded animal or, as many said, like the half-barbarian peasant he would always remain, he struck out at those around him. The officers who led the doomed attempts to scale the wall were executed in ever more inventive ways. Especial ingenuity was reserved for those from the nobility.

Ballista was even more hungry, thirsty and dirty than most. He was a tall youth, only sixteen winters and over six foot, and still growing. No one felt the lack of food more keenly than he did. His long blond hair hung lank down his back. A residual squeamishness held him back from washing on the riverbank. Since yesterday, a smell of burning, a reek of charred flesh, had joined the other odours which hung about him.

Despite both his youth and his status as a diplomatic hostage for his tribe, it had been considered by everyone the right thing that one of his birth, one of the Woden-born, should lead one of the units of German irregulars. The Romans had calculated the height of the wall, they had issued ladders of the correct length and, with Ballista at the front, the five hundred or so expendable barbarians had been sent off. The men had advanced at a jog, bent forward into the storm of missiles. The large bodies of the Germans and their lack of armour had made them good targets. Again and again there was a sickening sound as a missile struck home. They had fallen in droves. The survivors had pushed on in brave style. Soon the smooth walls had towered above them. More had fallen as they put aside their shields to raise the ladders.

Ballista had been one of the first to mount. He had started to climb one-handed, his shield held above him, his sword still in its scabbard. A falling stone had hit the shield, almost knocking him off the ladder. The noise was indescribable. He saw a long pole appear over the wall and push out over the next ladder along. At the end of the pole was a large amphora. Slowly the pole was turned, the amphora tipped, and a flaming mixture of pitch and oil, sulphur and bitumen poured like rain on to the men on the ladder. Men screamed, their clothes burning and shrinking, clinging to them, their flesh roasting. One after another they fell from the ladder. The incendiary liquid splashed out over those at its foot. They beat at the flames with their hands, rolled themselves on the ground. There was no way to put out the flames.

When Ballista looked up there was another amphora above his head, its pole beginning to turn. With no hesitation Ballista threw himself from the ladder. He landed hard. For a moment he thought that his ankle was broken or turned and that he would be burnt alive. But self-preservation had overcome the pain and, yelling for his men to follow him, he ran away.

Ballista had been thinking for some time that a conspiracy was inevitable. Impressed as he was by Roman discipline, no body of fighting men would put up with this siege for long. And after the disaster that day, he had not been surprised when he was approached.

Now, as he waited to play his part, he realized the depth of his fear. He had no wish to play the hero. Yet he had no real choice. If he did nothing, either Maximinus Thrax would execute him or the conspirators murder him.

A nod from one of the conspirators, and Ballista set off towards the huge purple tent with the standards outside. Suddenly he was very aware of what a beautiful day it was; a perfect Italian early June day, hot with a light breeze. A honey bee buzzed across his path. Swallows were wheeling high above.

A praetorian guardsman blocked Ballista’s way with his spear. ‘Where do you think you are going, barbarian?’

‘I need to talk to the emperor.’ Ballista spoke reasonable if heavily accented Latin.

‘Who does not?’ The praetorian was uninterested. ‘Now fuck off, boy.’

‘I have information of a conspiracy against him.’ Ballista dropped his voice. ‘Some of the officers, the nobles, are plotting to kill him.’ He watched the guardsman’s evident indecision. The potential danger of not passing on to a suspicious and vengeful emperor news of a possible conspiracy eventually overcame the natural fear of waking an increasingly short-tempered and violent man for whom things were not going well.

‘Wait here.’ The praetorian summoned a fellow soldier to watch the barbarian and disappeared into the tent.

He reappeared in short order and told the other praetorian to disarm and search the barbarian youth. Having given up his sword and dagger, Ballista was ushered into the tent; first into an antechamber, then into the inner sanctum.

At first, Ballista could see little. The purple gloom in the depths of the tent was profound after the bright sunlight outside. As his eyes adjusted he made out the sacred fire that is always carried before the reigning emperor burning low on its portable altar. Then he could see a large campbed. From it rose the huge pale face of the Emperor Caius Julius Verus Maximinus, commonly known as Maximinus Thrax, Maximinus the Thracian. Around his neck glittered the famous golden torque which he had won for his valour as a private soldier from the Emperor Septimius Severus.

From the far corner of the tent a voice snapped, ‘Perform adoration, proskynesis.’ As Ballista was pushed forward on to his knees by the praetorian, he saw Maximinus Thrax’s handsome son walk out of the darkness. Ballista reluctantly prostrated himself on the ground, then, as Maximinus Thrax held out his hand, kissed a heavy gold ring set with a gemstone cut with an image of an eagle.

Maximinus Thrax sat on the edge of the campbed. He was wearing just a simple white tunic. His son stood by his side, wearing his customary, elaborately ornamented, breastplate and ornamental silver sword, its handle in the shape of the head of an eagle. Ballista remained on his knees.

‘Gods, he stinks,’ said the son, putting a perfumed cloth to his nose. His father waved a hand to silence him.

‘You know of a plot on my life.’ Maximinus Thrax’s great grey eyes looked into Ballista’s face. ‘Who are the traitors?’

‘The officers, most of the tribunes and a few of the centurions, of Legio II Parthica, Dominus.’

‘Name them.’

Ballista looked reluctant.

‘Do not keep my father waiting. Name them,’ said the son.

‘They are powerful men. They have many friends, much influence. If they hear that I have denounced them, they will do me harm.’

The big man laughed, a horrible grating sound. ‘If what you say is true, they will be in no position to harm you or anyone else. If what you say is not true, what they might want to do to you will be the least of your concerns.’

Ballista slowly named a string of names. ‘Flavius Vopiscus, Julius Capitolinus, Aelius Lampridius.’ There were twelve names in all. That they were the real names of the men in the conspiracy hardly mattered at this stage.

‘How do you know these men want to kill me? What proof do you have?’

‘They asked me to join them.’ Ballista spoke loudly, hoping to distract attention from the growing noise outside. ‘I asked them for written instructions. I have them here.’

‘What is that row?’ Maximinus Thrax bellowed, his face twitching with habitual irritation. ‘Praetorian, tell them to be quiet.’ He held out a huge hand for the documents that Ballista proffered.

‘As you can see -’ Ballista continued.

‘Silence,’ ordered the emperor.

Rather than abating, the noise outside the tent grew. Maximinus Thrax, his face now contorted with rage, turned to his son. ‘Get out there and tell them to shut the fuck up.’

Maximinus Thrax read on. Then a surge of noise made him lift his pale face. On it Ballista read the first glimmer of suspicion.

Ballista leapt to his feet. He grabbed the portable altar bearing the sacred fire and swung it at the emperor’s head. Maximinus Thrax caught Ballista’s wrist with an unbelievably strong grip. With his free hand he punched him in the face. The youth’s head snapped back. The big man hit him in the stomach. Ballista collapsed in a heap. With one hand the emperor pulled Ballista back to his feet. He brought his face, a face like a rock, close to Ballista’s. His breath stank of garlic.

‘You will die slowly, you little fucker.’

Maximinus Thrax threw Ballista away almost casually. The youth crashed through some chairs and overturned a camp table.

As the emperor picked up his sword and headed towards the door, Ballista desperately tried to get some breath in his lungs and struggle to his feet. He looked around for a weapon. Seeing none, he picked up a stylus from a writing desk and stumbled after the emperor.

From the antechamber, the whole scene outside was framed and brightly lit as if it were a painting in a temple or portico. In the distance, most of the praetorians were running. But some had joined the legionaries of Legio II and were pulling the imperial portraits down from the standards. Nearer, there was a thrashing tumult of bodies. Just beyond the threshold was the mighty back of Maximinus Thrax. Sword in hand, his huge head turned this way and that.

The tumult stopped, and above the crowd rose the severed head of Maximinus Thrax’s son, stuck on a spear. Even smeared by dirt and blood it was still beautiful.

The noise the emperor made was not human. Before the big man could move, Ballista launched himself unsteadily at his back. Like a beast hunter in the arena trying to despatch a bull, Ballista stabbed the stylus down into Maximinus Thrax’s neck. With one mighty sweep of his arm, the big man smashed Ballista back across the antechamber. The emperor turned, pulled out the stylus and hurled it, bloodied, at Ballista. His sword raised, he advanced.

The youth scrabbled to his feet, grabbed a chair, held it in front of him as a makeshift shield and backed away.

‘You treacherous little fucker, you gave me your oath - you took the military oath, the sacramentum.’ Blood was flowing freely down the emperor’s neck, but it did not seem to be slowing him down. With two strokes of the sword he smashed the chair to pieces.

Ballista twisted to avoid the blow but felt searing agony as the sword thrust scraped down his ribs. On the floor now, holding his arms to the wound, Ballista tried to shuffle backwards. Maximinus Thrax stood over him, readying himself to deliver the killing blow.

The thrown spear punched into the emperor’s unprotected back. He staggered an involuntary step forward. Another spear slammed into his back. He took another step, then tipped over, landing on Ballista. His enormous weight was crushing the youth. His breath, hot and rank, was on Ballista’s cheek. His fingers came up to gouge the boy’s eyes.

Somehow, the stylus was back in Ballista’s right hand. With a strength born of desperation the youth drove it into the emperor’s throat. Blood sprayed out. The emperor’s fingers jerked back. Blood stung Ballista’s eyes.

‘I will see you again.’ The big man uttered his final threat with a hideous grin, blood gurgling and foaming from his twisted mouth.

Ballista watched as they pulled the body outside. There they fell on it like a pack of hounds breaking up its quarry. His head was hacked off and, like that of his son, hoisted on a spear. The huge body was left for anyone to trample on and desecrate, for the birds and dogs to tear to pieces.

Much later, the heads of Maximinus Thrax and his son were sent to Rome to be publicly exhibited. What was left of their bodies was thrown in the river to deny them burial, to deny rest to their spirits.