Raising his hands to heaven, the emperor sent heartfelt words of supplication and entreaty winging to the throne of God. His voice rang out in the twilight stillness with all the passion of a commander who knows his troops woefully outnumbered and must trust their courage to sway the scales of war.

When at last the emperor finished, night had descended upon the camp. Alexius opened his eyes and stood to gaze in amazement at a most miraculous sight; it was as if the stars above had fallen to earth, and the plain before him now sparkled with all the glory of heaven itself. Each and every soldier had a lighted wax taper affixed to the blade of his spear-fifty thousand earthstars shining with bright-flecked rays, illuminating the camp with a clear and holy light.

The glow from that light sustained Alexius through the long, restless night, and was with him still when he rode out at the head of his troops before dawn. The imperial cavalry crossed the Maritsa a few miles upstream of the encamped enemy, formed the battalions, and waited for daybreak. They attacked from the east, with the light of the rising sun at their backs. To the sleep-sotted barbarians, it seemed as if the warhost of heaven was streaming down upon them from out of the sun.

Alexius struck the confused mass at the centre of the Pecheneg and Bogomil horde. It was a swift, sharp thrust into the belly of the beast, and he was away again before the barbarian battlehorns had sounded the call to arms. Having roused and enraged the enemy, he fell back – just out of reach of their slings and spears-and waited for them to make their counter attack.

The invaders, eager to avenge the assault, hastily formed a battleline and began their plodding advance. The imperial defenders looked out on a single vast, clotted mass of bellowing barbarians -less an ordered line than an enormous human tidal wave rolling across the land-and heard the deep jarring bone-rattling thump of the drums, the strident, sense-numbing blare of the huge, curved battlehorns, and the defiant cries of the warriors as they swept towards them with quickening pace.

It was a display calculated to produce terror in the beholder; it was their chief weapon, and one which served them well; with it, they had conquered tribe and nation, overrunning all they surveyed. The empire's soldiers had faced it before, however, and the sight and sound of barbarians massing for their attack no longer inspired shock or dismay, no longer quelled the heart in terror, or swallowed the senses in panic. The Immortals gazed with narrowed eyes and tightened their grip on lances and reins, calmed their horses with gently whispered words, and waited.

Flanked on either side by his standard-bearers-one lofting the purple banner of the Holy Roman Empire, the other the golden vexillum-Alexius looked across to his officers, the strategi, who anchored the long ranks at the centre of either wing. The foremost of these was a seasoned veteran of the Pecheneg wars, a man named Taticius, whose fearlessness and shrewdness had often saved lives and won battles. The emperor signalled his general, who sang out in a strong voice: 'Slow march!' *

The trumpets sounded a single, shrill blast, and the troops started forth as one. The imperial formation-two divisions, each made up of ten regiments in ranks, five deep, and a hundred riders to the rank – moved in close concert with one another; shoulder to shoulder and knee to knee, the riders formed a wall not easily breached or broken. Their long lances kept the foe out of reach of their horses, and themselves out of reach of barbarian axes and war hammers. Once in motion, there was little on the ground that could withstand a charge of mounted warriors.

Taticius gave the sign, the trumpets blared again, and the riders quickened their pace. The invaders met this with a shout, and came on. Fifty paces later, the trumpets sounded a third time, and the riders doubled their speed. The horses, trained to combat, strained at the reins, excited for the coming clash; but the riders held them back, waiting for the signal.

Faster and faster came the barbarians, the sound of their screams and drums and horns shaking the very earth and air, drowning out the thunder of the onrushing hooves. At the strategus' signal, the trumpets shrilled once more. Ten thousand lances swung level.

The two forces closed upon one another at speed. As the gap swiftly narrowed, the trumpets gave out a last signal and the horsemen put spurs to their mounts and let them run.

For the space of two heartbeats, the world was a churning chaos of blurred motion as the two onrushing armies fell upon each other. The clash sounded a mighty crack which echoed from the surrounding hills, and ten thousand barbarians fell. Many of these were trampled down and their brains dashed out beneath the iron hooves of the emperor's horses; the rest met death at the point of a Byzantine spear.

The charge carried the emperor and his troops deep into the barbarian mass. The screaming hordes, seeing the gleaming gold and purple standards, leapt over one another in their frenzy to strike down the Elect of Heaven. But Alexius, mindful of the danger of allowing the enemy to surround his division, had instructed Taticius to signal the retreat as soon as the assault foundered. Accordingly, the trumpets sounded above the barbarian shriek and, with practised ease, the imperial soldiers disengaged, fleeing back over the bodies of the dead and dying.

The enemy, seeing the horsemen turn away, pounded on in blood-blind pursuit, screaming as they ran. They chased the fleeing horsemen-only to be met with another measured charge by oncoming cavalry. The emperor, having had time to halt the retreat, had turned his troops and reformed the ranks; Alexius, with five thousand horsemen behind him, spurred his division into the centre of the oncoming barbarian battlehost.

The barbarians, neither so quick nor so tightly clumped as before, were more cautious this time. They tried to dodge the spears and hooves, to allow the horses to pass and stab at the riders as they swept by. The Byzantines had long acquaintance with this tactic, however, and were not easily outflanked. The ranks behind covered for the line ahead, and the barbarians could not close on those they sought to strike. Indeed, most were fortunate not to be cut down as they darted into position.

The charge ground to a halt, and the imperial troops made good their retreat, falling back the instant the attack faltered. They fled back across a battleground now deep with Pecheneg and Bogomil dead. This time, however, they did not regroup and charge again, but fled up the hill.

The enemy, believing they had beaten the Byzantines, quickly reformed the line. The drums began beating, and the horns blaring, and they marched ahead once more, but slowly this time. Two disastrous charges had taught them respect for the elusive horsemen.

Nicetas, who had been waiting on the hilltop, joined the emperor, and said, 'The Cuman are growing restless, Basileus. They say that if they are not allowed to fight before midday, they will leave the battlefield.'

'It is a long time to midday,' Alexius replied. 'Their patience is soon rewarded. See here!' He pointed to the approaching horde. No longer a single amorphous line, the barbarians had separated themselves into three distinct bodies, each under the leadership of a battlechief. 'Tell our vengeful friends that we will soon deliver their enemies into their hands. Warn them to be vigilant.'

Nicetas saluted, turned his horse and galloped back to his position. The emperor returned to the head of his troops to lead the next assault. Aware that he was embarking on the most dangerous phase of the battle, Alexius uttered a brief prayer and crossed himself. Reining in among his standard-bearers once more, he signalled to Taticius, who turned and shouted the order: 'Slow march!'