‘I have been thinking of this too, and I think it may have been an earthquake, the fall of a mountain or a mighty cliff, perhaps far far away,’ Ishraq said, surprisingly. ‘Perhaps it caused a wave, just one great wave, as a bowl of water will make waves and spill over, if you were to throw a stone into it.’

Brother Peter rose to his feet and smiled at the prosaic image, typical of a woman who cannot imagine the earth as void and empty, and darkness upon the face of the deep; and the spirit of God moving over the waters, as the Bible itself describes. ‘The ocean is not a bowl of water,’ he corrected her gently. ‘It does not move with waves because someone throws a stone. It is not rocked in a basin for you to wash dishes in.’

‘I am not saying that it is. But small things sometimes work the same way as larger. The wave may have been caused by an earthquake, a great falling of rock. Just as you can make a wave in a bowl of water if you throw in a pebble.’

‘That’s true,’ Luca said. ‘But what made you think of this?’

‘Plato describes the drowning of the country of Atlantis in just such a way,’ she said. ‘He says that a great earthquake caused a great wave which drowned the island.’

‘Plato?’ Brother Peter repeated sceptically. ‘How has a girl such as you read Plato? I’ve heard of him, but I’ve read nothing that he wrote. There are no copies of anything he wrote.’

‘No, not that you could read, not translated into Italian; but we Arabs have his books. A few of them have been translated from the Greek into Arabic. I read a little part of them in Arabic when I was in Spain, with Isolde and her father, and I was allowed to attend the university. Plato is a philosopher who talks about great mysteries such as the wave, and has strange understandings.’

‘You were privileged,’ Brother Peter said irritably scooping up the papers and stoppering the bottle of ink. ‘A heretic and a woman to read such a thinker. You must take care that it does not strain your nature, putting too much pressure on you. Women cannot think of abstractions..’

She gave a small shrug. ‘My brain is well enough so far, though I thank you for your concern. At any rate, Plato says that the drowning of Atlantis might have followed a great movement of the earth. It made me think that this might be a natural occurrence, not an act of God, nor of the devil, nor of storm-bringers – if there are such people. Perhaps it occurs naturally, from the world of nature. Though why God would make a world where such a thing could happen, is another question.’

Brother Peter knew himself to be on firmer ground. ‘Ah, you ask an important question. It is because the perfect world that God first made was destroyed by sin in the garden of Eden, when the woman ate the apple.’