Gwalchavad reached the three on the hill and fell to work beside them at once.

At the appearance of Gwalchavad running out upon the hillside, the floodgates opened and others began moving from the cover of the wood. By twos and threes they went, then by dozens and scores to see what was happening.

'Well, Gwalchavad has persuaded them beyond all doubt,' Cai observed. 'What are we to do now? Our army is advancing without us.'

Llenlleawg turned to me. 'It is the supreme dishonour for a battlechief to fall behind his warriors."

'Cai, are we to be taught our duty by an Irishman?'

'Never!' Cai cried. 'Flay me for a Pict! I will not have it flaunted about that we neglected our duty.'

'Brave Cai,' I said, 'foremost in war and wall building!'

Together we marched from the wood. Llenlleawg fell into step beside us. I confess, I had begun to warm to that man. He was Irish, there is no denying it, but a deal less vile than others of his race. The soul within him was noble, and his heart was true. More the shame for men like Cerdic: when the barbarian reveals higher nobility than right-born Britons!

We advanced to where Arthur and the others laboured at the rocks. 'What do you here, Bear?' I asked.

Arthur straightened. 'I am building a wall.'

'This we have observed,' said Cai. 'Are we to know the reason for this unseemly toil?'

The Duke hefted a stone and lifted it above his head. He stepped onto the pile of rocks he had raised. 'Men of Britain!' he called. 'Listen to me!'

Warriors pressed close to hear him. The cold wind fluttered the red cloak about Arthur's shoulders; mist pearled in his hair. 'Look in my hand and tell me what you see.'

'A stone!' they cried. 'We see a stone!'

Arthur lofted the stone before them. 'No, I tell you it is not a stone. It is something stronger than stone, and more enduring: it is a prayer!

'I tell you,' Arthur continued, 'it is a prayer for the deliverance of Britain. Look around you, my brothers; this hillside is covered with them!'

We scanned the rough and rocky steeps of Baedun as Arthur directed. Baedun was, as he said, covered with stones – as if we had not known this already!

'You ask what I am doing. I will tell you: I am gathering up the prayers and making a wall with them. I am raising a stronghold to surround the enemy.

'Our Wise Emrys has decreed that we must erect a fortress whose walls cannot be battered down or broken – a caer that cannot be conquered. My countrymen, that is what I am doing. When I have finished, not a single barbarian will escape.'

With that Arthur stepped down and placed his stone upon the pile he had made. Men regarded him as if he had become mad. The wind whipped through the crowd and uttered sinister whispers against the Duke. The silence grew dense with accusation: he is mad!

Then, throwing his cloak over his shoulder, Cai stooped and, every sinew straining, lifted an enormous rock and, grinning with the exertion, heaved his rock on top of Arthur's. It fell with a solid and convincing crack. 'There!' Cai declared loudly. 'If stones be prayers, I have sung a psalm!'

Everyone laughed and suddenly other stones began toppling onto the pile as one by one we all stooped to the stones at our feet and lifted them to top the foundation Arthur had made. In this way, the wall was begun.

The lords of Britain held themselves aloof from this toil, but when they saw the fervour of their men, and the zeal of the Cymbrogi, they put off their cloaks and directed the work. It was a triumph to see them – Ennion and Custennin, Maelgwn and Maglos and Owain, Ceredig and Idris, all of them barking orders and urging on the men.

We are a song-loving people and labour is long without a melody to lighten it. Once the work began in earnest, the singing began. Holy songs at first, but when these gave out we turned to the simple, well-known songs of hearth and clan – and these I believe are holy too. The wall rose stone by stone, each stone a heartfelt prayer.

High up in the hilltop stronghold, the barbarians looked down upon our strange labour. At first they did not know what to make of it, and then as the line of the wall appeared and stretched along the hillside, they began to shout and jeer. When the wall began to rise, their jeers became angry taunts. They threw stones and shot arrows at us, but we were beyond hurtful range and the stones and arrows fell spent long before reaching us. They raged, but they did not leave the protection of their fortress.

Now, two men working diligently can raise a twenty-pace section chest high in a day. How much more, then, can three thousand times that many accomplish? Saints and angels, I tell you that wall raised itself, so quickly did it appear!

See it now: hands, thousands of hands reaching, grasping, lifting, placing, working the rough stone into a form.

Backs bending, muscles straining, lungs drawing, cheeks puffing with the effort, sweat running. Palms and knuckles roughened, fingers bleeding. The wind billowing cloaks, rippling grass, curling mist and rain.

Dusk fell full and fast. And though dark clouds swirled about the hilltop, light, clear and golden, shone in the west. In that light's last gleam we placed the final stone on the wall and stood back to see what we had done. It was marvellous to behold: a long, sinuous barrier rising to shoulder height and surrounding the entire hill.

The enemy wailed to see it. The barbarians howled in frustration. They cursed. They screamed. They saw themselves surrounded by stone and called upon one-eyed Woden to save them. But their cries were seized by the wind and flung back in their faces. The wall, Arthur's Wall, stood defiantly before them, encircling Baedun with its stern message: you will not leave this battle ground. Here you will die, and here your bones will lie unmourned for ever.

My arms ached, and my legs and feet and back. My hands were scraped raw; my arms were cut. But I looked upon that wonderful wall and my small agonies were less than nothing. It was more than a wall – it was faith made manifest. I looked upon the work of our hands and I felt invincible.

The barbarians looked upon the wall and despaired. For they saw that Arthur had cut off his own retreat – no one does that who doubts the victory. Thus was Arthur telling them: your doom is sealed; you are lost. They keened their death songs into the gathering gloom. And then, though the day was far spent, they attacked.

Why they waited so long I will never know. Perhaps God's hand prevented them. Perhaps Arthur's Wall of Prayer daunted them. But all at once they swarmed out from their stronghold and flew down the hill towards us. Rhys signalled the alarm and we snatched up our weapons, turned and formed the line, then raced to meet them. The shock of the clash shuddered the mountain to its roots.

Fighting at night is difficult and strange. The enemy has a shape, but no face; a body of limbs, but no features and no definite form. It is like fighting shadows. It is like one of those Otherworldly battles the bards sing about, where invisible armies meet in endless combat on a darkling plain. It is strange and unnatural.

We fought, though exhaustion hung like a sodden cloak upon us. We fought, knowing that all our work would be for nothing if we could not now shake off our fatigue and keep the enemy from reaching the wall. Indeed, the barbarians seemed more intent on gaining the wall than in fighting us. Perhaps they thought to escape. Or perhaps they saw in Arthur's Wall something which they could not abide – something they feared worse than defeat or death.

Gloom enwrapped the hill. The wind shrieked in our ears and rain drove down. The barbarian host pressed us back and back. Heedless of danger, heedless of death, they swarmed before us, driving at us out of the storm-tossed darkness. On and on and on they came, torches flaming, forcing our backs to the wall our hands had raised.