But it was the horseman I watched. He rode so awkwardly and I could see now that he was tied onto the horse. His ankles were linked under the stallion’s black belly with rope, and his body was fixed to the saddle by what had to be strips of timber clamped to the saddle’s tree. He had no helmet so that his long hair flew free in the wind, and beneath the hair the rider’s face was nothing but a grinning skull covered by desiccated yellow skin. It was Gawain, dead Gawain, his lips and gums shrunken back from his teeth, his nostrils two black slits and his eyeballs empty holes. His head lolled from side to side while his body, to which the dragon banner of Britain was strapped, swayed from side to side.

It was death on a black horse called Anbarr, and at the sight of that ghoul coming at their flank, the Saxon confidence shuddered. The Blackshields were shrieking behind Gawain, driving the horse and its dead rider over the hedges and straight at the Saxon flank. The Blackshields did not attack in a line, but came in a howling mass. This was the Irish way of war, a terrifying assault of maddened men who came to the slaughter like lovers.

For a moment the battle trembled. The Saxons had been on the point of victory, but Arthur saw their hesitation and unexpectedly shouted us forward. ‘On!’ he shouted, and ‘Forward!’ Mordred added his command to Arthur’s, ‘Forward!’

Thus began the slaughter of Mynydd Baddon. The bards tell it all, and for once they do not exaggerate. We crossed our tide line of dead and carried our spears to the Saxon army just as the Blackshields and Culhwch’s men hit their flank. For a few heartbeats there was the clangour of sword on sword, the thump of axe on shield, the grunting, heaving, sweating battle of locked shield walls, but then the Saxon army broke and we fought among their shredding ranks in fields made slick with Frankish and Saxon blood. The Saxons fled, broken by a wild charge led by a dead man on a black horse, and we killed them until we thought nothing of killing. We crammed the bridge of swords with Sais dead. We speared them, we disembowelled them, and some we just drowned in the river. We took no prisoners at first, but vented years of hatred on our hated enemies. Cerdic’s army had shattered under the twin assault, and we roared into their breaking ranks and vied each other in killing. It was an orgy of death, a welter of slaughter. There were some Saxons so terrified that they could not move, who literally stood with wide eyes waiting to be killed, while there were others who fought like demons and others who died running and others who tried to escape to the river. We had lost all semblance of a shield wall, we were nothing but a pack of maddened war-dogs tearing an enemy to pieces. I saw Mordred limping on his clubbed foot as he cut down Saxons, I saw Arthur riding down fugitives, saw the men of Powys avenging their King a thousandfold. I saw Galahad cut left and right from horseback, his face as calm as ever. I saw Tewdric in a priest’s robes, skeletally thin and with his hair tonsured, savagely slashing with a great sword. Old Bishop Emrys was there, a huge cross hanging about his neck” and an old breastplate tied over his gown with horsehair rope. ‘Get to hell!’ he roared as he jabbed at helpless Saxons with a spear. ‘Burn in the cleansing fire for ever!’ I saw Oengus mac Airem, his beard soaked with Saxon blood, spearing yet more Sais. I saw Guinevere riding Mordred’s horse and chopping with the sword we had given her. I saw Gawain, his head fallen clean off, slumping dead on his bleeding horse that peacefully cropped the grass among the Saxon corpses. I saw Merlin at last, for he had come with Gawain’s corpse, and though he was an old man, he was striking at Saxons with his staff and cursing them for miserable worms. He had an escort of Blackshields. He saw me, smiled, and waved me on to the slaughter.