Arthur gazed on this sight for a long moment, and then turned to the waiting troops behind us. 'The enemy is before us, brothers!' he cried. There is glory to be won! For Holy Jesu and Britain!'

Lofting his spear in the air, Arthur signalled Rhys, who raised the hunting horn to his lips and gave forth a rousing blast. Arthur turned his horse and began trotting towards the ford. He had no need of ordering the warbands. We all knew what to do. The armies of Britain arrayed themselves even as we flew to join the enemy – the a/a in a strong double line going before; the foot soldiers, seven thousand in all, advancing behind.

The earth trembled with the pounding of hooves and the drumming of feet. The sun blazed high overhead in a blue-white haze of sky. The ford spread before us the colour of hard iron, and beyond it the innumerable ranks of the foe-men. Before that day, I had never seen so many barbarians in once place.

The thunder of our charge was nothing to the world-splitting lightning of our clash. Saints and angels bear witness! The foe scattered before us like sheep – retreating from the first charge!

We pursued them as they fled into the forest, and learned too late the reason for their seeming cowardice.

Row upon row of sharpened stakes had been planted on the forest fringe. The cruel shafts tore at the legs and ripped the bellies of the horses. We lost scores before we could halt the charge. Down they went, the ranks riven by the brisk brutality of the trap. All around me were men and horses impaled upon those hateful pikes.

Fortunate were those who died outright. The screams of agony were terrible to hear. More terrible still was the sight of those brave horses and riders thrashing, struggling to free themselves from the death trap, their flanks and chests pierced by the wicked stakes; the blood and entrails of the brave spilling freely upon the earth.

I was saved only by the narrowest chance. To think of it chills the marrow in my bones even now. I saw the brutal stakes before me and jerked back the reins with all my strength, lifting my mount's head and forelegs in an insane leap. The nearest stake raked the hide from the animal's belly, but we landed untouched in the only clear place that I could see for dozens of paces in any direction.

The cold cunning of the barbarians took us by surprise. They feared our horses, and that fear inspired them to new depths of savagery. At the sight of our ala faltering in bewilderment, our precise formation collapsing in chaos, the enemy roared in delight and leapt upon our helpless warriors. They hacked the defenceless with their sharp war axes, and Sung the severed heads at us.

Carefully, carefully, we fought through the trap, picking our way among the stakes, advancing slowly over the bodies of our own. The enemy gave ground, but stubbornly. Each small advance was made at heavy cost.

And then we were through the trap and into the forest. And here the barbarians triggered the second of their deadly stratagems. For, the moment we cleared the forest's edge, the foe turned and ran, vanishing into the wood.

We had no choice but to follow if we were to maintain our advantage. So we plunged blindly after them. This was our second mistake.

As I have said, the barbarians had laboured through the early summer, and as we drove deeper into the forest the fruit of those labours became apparent. All summer they had hewed trees and delved soil to build a perfect mazework of earth and timber. They had opened ditches and constructed elaborate walls and barriers against us.

We careened into the forest, storming headlong into the ditches and walls. The barbarians stood on top of the timbers and hurled stones and tree trunks down upon us. Suddenly we discovered our attack halted and overwhelmed. In a single swift moment our horses were made useless and we were impossibly outnumbered.

Yet we fought doggedly on. We charged the barriers and threw ourselves against them as if to break them down by force of will alone. We slew and were slain, but could gain no advantage. The cunning barbarian mazework kept us separated and confused. We tried to circle round the earthworks, to breach the furthest edge, but the forest prevented us. It was too thick and the way too easily lost. So we charged the barriers. Again and again and again… we were thwarted. Each time we came away leaving more dead in the ditches than the time before. Our efforts grew erratic, frantic, reckless.

Arthur had no choice but to order the retreat. Rhys blew the long quavering note and riders began streaming past me out of the wood. Arthur was last among them.

'We can do nothing against this,' he said, his voice husky with fatigue. 'We must find another way.'

Out of the forest, I saw our troops streaming across the ford. It was a dismal sight. Battered bloody, and limping with exhaustion, they dragged themselves to the far bank and collapsed. Food and drink had been prepared by the camp cooks and these were hastily brought and given the warriors where they dropped.

Rhys sounded assembly, and the battlechiefs sought us where Arthur had planted his spear on the riverbank. Grim-faced, they slid from their saddles, wiping sweat and blood from their eyes. The lords came to stand in a ring, with Arthur at the centre.

The curses with which they greeted the Duke spoke their despair. They blamed Arthur for the retreat, or rather its necessity, and wasted little time telling him how they felt about it. Arthur took their abuse, but the Emrys frowned and raised his staff.

'Did you think yourselves invincible?' inquired Myrddin sourly. 'No? Then why condemn Arthur for your own weakness?'

'Weakness!' Idris cried. 'You blind bastard! I own no fault in this. Half my warband was cut down by those cursed stakes.'

Ceredig grumbled agreement, and Owain tactfully suggested, 'Our War Leader should have known better.'

'Did you know better?' I demanded hotly. 'Or you, Ceredig? Ogryvan? I did not hear your protests when Arthur laid die battle plan.'

'It is our fault, is it?' wailed Maglos, his voice thin and pathetic. They were hurting and did not know what they were saying, it is true, but it rankled me to have them blame Arthur.

'I cannot see it serves any purpose to accuse each other – ' began Custennin, his voice quickly drowned in the railings of the others.

Myrddin made to speak again, but Arthur laid his hand on the Emrys' arm. 'I am with you, my lords," he declared loudly, so as to be heard above them. 'I should have seen the traps sooner. I should have guessed. I own the fault. But we are in it now and must decide what is best to do. We are beaten where we stand if we fall to fighting among ourselves.'

'Hear him!' said Custennin and several others. Meurig added, 'Let us save our fury for the foeman.'

Tempers were brought to heel, and a sullen silence settled over the lords. The stewards came with cups and we were given cold water to drink. 'Now then,' began Arthur, draining his cup in a gulp, 'what did you want to say to us, Wise Emrys?'

‘The pit that snares the wolf, may also capture the hunter. And there are many, many traps in Celyddon,' Myrddin said.

'Spare us your riddles, Bard,' growled Idris.

'What the Emrys means,' explained Arthur, 'is that perhaps we can turn the traps to our advantage.'

'How?' demanded the surly kings. 'Our horses are no use to us in the wood. You can scarce swing a sword without tangling blade and arm in the branches.'

'You are right,' soothed Arthur. I looked and saw the light come up bright and fierce in his eyes. 'Listen, Baldulf thinks to use the forest against us; very well, we will take up the weapons of the forest: darkness and disguise, secrecy and stealth.'

I do not know how Arthur did this. Was it in his mind, waiting to be called forth at need? Did it come to him fresh from the Otherworld – like the awen of a bard? Or did he simply invent it as he spoke it out? As many times as I saw him do it, I cannot say. But when at need a plan of genius was required, genius we received.