There has been a fortress at Trath Gwryd from ancient times. Like Caer Alclyd on the west coast and Caer Edyn on the east, it is built atop an enormous rock above a river, and stands between them in the centre of the invasion route. And like Caer Alclyd the Picti had seized the old rock-top fortress, intending to defend it against us.

Upon reaching the sands of Gwryd, below the rock, we camped and laid siege to the rock. Almost at once Arthur's scouts began returning with further reports about the enemy siege at Caer Edyn: Ectorius still held the fortress, and seemed in no immediate danger; the stronghold remained solid and secure.

King Custennin of Celyddon arrived with more disturbing news: others were coming into the war. Along with the Angli there were Jutes, Mercians and Frisians from across the northern sea; Scoti and Attacoti from Ierne; and Cruithne joining with the blue-painted Picti. In short, all the old enemies of Roman Britain. The new Bretwalda, whoever, he was, had stirred the pot well.

God's mercy, there were no Saecsens. Somehow the peace in the south held true, or the fight would have been finished before it began.

Anxious to move on to the defence of Ector at Caer Edyn as soon as possible, Arthur dealt with the rock fort quickly, using the same night raid tactic with which we had reconquered Caer Alclyd. The battle was short and sharp, and we prevailed. The fortress duly secured, we turned east to the rescue of Ectorius.

We passed through several small holdings and settlements along the way. The barbarians had been there before us and had left behind the black mark of their passing – a smouldering scar of destruction, bleak and terrible, a bleeding wound upon the land. Crops burned, cattle driven, goods plundered and carried off, and all else ruined.

Bitter smoke and ashes filled our mouths; tears filled our eyes. For in each of the holdings the bodies of men, women and infants lay strewn among the debris. Not content to fire the buildings and slaughter the people, at each place the barbarians left a grisly reminder of their cruelty and hate: a disembowelled corpse lying in the centre of the road, stomach carved open and lungs spread out upon the chest, liver pulled out and placed between the lungs, the heart severed and laid on top, the genitals cut off and stuffed in the mouth.

It was a sight to sicken, to dishearten, to taunt. Not a man among us who saw it failed to imagine himself or his sword brother or kinsman lying dead there – dismembered and dishonoured. Fear and humiliation were kindled by the ghastly spectacle and spread like a noxious stench through our ranks.

But, in each place where this atrocity was practised, Arthur acted forthrightly. He ordered the body to be wrapped in a clean cloak and decently buried, with prayers spoken over the body.

This helped ease our dismay, but did not banish it. Daunted and sick with dread we drew near Caer Edyn. Custennin had warned us, and we were ready. Yet the first sight of the besieging host encamped upon low hills below the caer stole the light from our eyes and the warmth from our hearts.

They were not lying when they told you the whole barbarian realm had come to Caer Edyn,' Cai said. 'How did so many escape our ships?'

Arthur's face hardened like flint. His eyes turned the colour of Yr Widdfa in storm. 'Breathe the air, my friends,' he said. We drew a deep breath of the fresh, salt-tinged breeze. 'It tastes of triumph, does it not?'

Seeing the black smoke curling into the blue-white sky and the loathsome masses swarming about the roots of Ector's strong fortress brought the sour gall to my lips. 'It tastes of death, Artos,' I replied.

'Death or triumph, I will embrace one or the other before this day is done.'

At this moment the barbarian host sent up a deafening screech. 'This sound, so hateful to our ears, will no more be heard in Britain,' observed Myrddin, sitting his horse, hands folded calmly before him. His golden eyes, as ever, were bound in a length of white linen. 'I have seen the face of the Bretwalda: it is a Briton's face and its features are well known to us all.'

This the Emrys spoke as if dropping a remark about barley bannocks. 'Is that all? A name! Tell us who it is, Wise One,' I said.

'The name you know already. I will not defile my tongue to utter it.'

'Wise Emrys,' pleaded Cai, 'I would hear spoken the name of the dog who has raised this outrage against my kinsmen.'

It was no use asking, Myrddin would say no more.

Arthur began at once to order the attack. Down on the narrow plain the enemy was already forming the battle line. I could see that they had chosen the field well. Even if they did not possess the fortress, the rock wall at their backs gave them good protection, and the deep-riven dells would make it difficult for our horses.

Nevertheless, the ala moved into position, forming three divisions of four ranks each. I led one division, Cai another, and Bors the third – each of us with two kings under our command. Arthur, with Llenlleawg beside him, would lead the warriors on foot – we all knew that once the horses had served their purpose the battle would be waged on foot.

At Rhys' signal we galloped forth, spears levelled, shields dressed. The thunder of hooves drummed in our brains and blood. I settled into the saddle, gliding with the rhythmic rock and sway of the fearless animal beneath me. My hand, my arm, my eye – all of my being became the sharp spearhead glinting at the end of the ashwood haft, slicing air before me.

Closing with merciless speed, the first rank went down before me, mouths agape, eyes wide in wonder and terror. As in all the other battles, I fought through the knotted confusion of bodies, the clash keen and loud in my ears, the blood mist in my eyes. I slew the enemy before me, taking them on the point of my spear. And when that broke, I used my sword.

I hewed mightily. I laboured like the fanner when the thunder and lightning threatens his ripe field. But no planter ever reaped such grim harvest, or gathered a loathlier crop.

We were lions! We were charging boars in battle! Our first attack, fierce and furious, broke the barbarian line in four places. It sagged inward as if to draw us in and crush us against Edyn's Rock – and well they might have, for there were more than enough of them! – but Arthur, swift and sure, drove into them from behind.

The barbarian resistance collapsed in chaos and they began to scatter. I steered my division back towards Arthur's position, carrying all before me. And then I saw it, springing up directly in my path – the Bretwalda's skull-and-bones standard. And beneath it, surrounded by his house carles, the Bretwalda himself. And, God help him, I recognized the face beneath the iron helm: Cerdic ap Morcant.

It was Cerdic!

Bile surged up into my gullet and into my mouth. Rage, hot and black, dimmed my sight. I lashed my mount forward, hoping to attack him before he saw me. But the craven's carles closed around him and bore him away before ever I could reach him. Indeed, the barbarians were scattering, fleeing south and west. Confusion must have gripped them, for they were running away from the coast where lay their ships!

I made directly for Arthur. 'I have seen him, Bear,' I shouted. 'I have seen the Bretwalda.'

His head whipped towards me. 'Who is it?'

'Cerdic ap Morcant,' I told him. 'I saw him with the Angli.'

Arthur bristled. 'That coward will curse the day of his birth,' he muttered. Then said, 'It is well. If he will not hold with me in life, let him keep faith with me in death. Either way, I will own his fealty!'

'Sound the pursuit! We can catch him,' I cried, preparing for the chase.

To my surprise, Arthur merely shook his head. 'No,' he said. 'I will not ride into ambush. Reform the a/a and care for the wounded, then gather the chieftains and come to me at the caer. I will hold council in Ector's hall.' He rode off, leaving me to sputter after him.