Emrys had gone to stand under the arcade, as though he feared the strength of the magic that flickered and flowed so bright across the stars. ‘All religions use death, Lord,’ he said pedantically, ‘even ours believes in sacrifice. It is just that in Christianity it was the Son of God who was killed so that no one again would ever need to be knifed on an altar, but I can think of no religion that does not use death as part of its mystery. Osiris was killed,’ he suddenly realized he was speaking of Isis’s worship, the bane of Arthur’s life, and hurried on, ‘Mithras died, too, and his worship requires the death of bulls. All our Gods die, Lord,’ the Bishop said, ‘and all religions except Christianity recreate those deaths as part of their worship.’

‘We Christians have gone beyond death,’ Galahad said, ‘into life.’

‘Praise God we have,’ Emrys agreed, making the sign of the cross, ‘but Merlin has not.’ The lights in the sky were brighter now; great curtains of colours through which, like threads in a tapestry, flickers of white light streaked and dropped. ‘Death is the most powerful magic,’ the Bishop said disapprovingly. ‘A merciful God would not allow it, and our God ended it by his own Son’s death.’

‘Merlin doesn’t use death,’ Culhwch said angrily.

‘He does,’ I spoke softly. ‘Before we went to fetch the Cauldron he made a human sacrifice. He told me.’

‘Who?’ Arthur asked sharply.

‘I don’t know, Lord.’

‘He was probably telling stories,’ Culhwch said, gazing upwards, ‘he likes to do that.’

‘Or more likely he was telling the truth,’ Emrys said. ‘The old religion demanded much blood, and usually it was human. We know so little, of course, but I remember old Balise telling me that the Druids were fond of killing humans. They were usually prisoners. Some were burned alive, others put into death pits.’

‘And some escaped,’ I added softly, for I myself had been thrown into a Druid’s death pit as a small child and my escape from that horror of dying, broken bodies had led to my adoption by Merlin.

Emrys ignored my comment. ‘On other occasions, of course,’ he went on, ‘a more valuable sacrifice was required. In Elmet and Cornovia they still speak of the sacrifice made in the Black Year.’

‘What sacrifice was that?’ Arthur asked.

‘It could just be a legend,’ Emrys said, ‘for it happened too long ago for memory to be accurate.’ The Bishop was speaking about the Black Year in which the Romans had captured Ynys Mon and so torn the heart from the Druids’ religion, a dark event that had happened more than four hundred years in our past. ‘But folk in those parts still talk of King Cefydd’s sacrifice,’ Emrys continued. ‘It’s a long time since I heard the tale, but Balise always believed it. Cefydd, of course, was facing the Roman army and it seemed likely he would be overwhelmed, so he sacrificed his most valuable possession.’