Roger Bacon seemed to care nothing for that. Saladin saw he was fired only by his curiosity, by the scent of fresh knowledge in his nostrils. ‘You must retrieve these designs,’ he said rapidly. ‘And you must bring them to me. What you need to make all this work is a dominus experimentorum. Such as myself, or an assistant. I can see it now. A scheme of work designed around two elevating principles. First, the verification of the designs, and the physical principles on which they have been based, perhaps principles hitherto unknown to mankind and therefore an everlasting gift to scholarship. Second, the use to which the new understanding may be put, which is the protection of Christendom, and thereby the spiritual welfare of all mankind and the greater glory of God.’

Thomas said, ‘You would think, brother, from what you say, that you were being asked to make cathedrals, not weapons.’

‘There is no sin in using the power of the mind to build weapons to fight a just war. Why, your Weaver must be a Christian, or he would not have put these engines into the hands of Christians. How can this not be God’s work?’

‘I know very little about the Weaver, and you know less,’ Thomas said sternly. ‘You must ensure you discuss this work with your confessor, brother. Fully and regularly.’

‘Yes, yes.’ Bacon leaned towards Joan, eyes bright, like the cat’s into which he had spent long hours staring, Saladin thought. ‘Bring me your plans, lady. By God’s bones, there is no other way - indeed it must be divine providence that brought you to me.

‘Give me your plans,’ said Roger Bacon, ‘and I will build the Engines of God for you.’

XXIII

XXIII

AD 1248

The guard brought the two of them to Ibrahim’s office: the accuser, a middle-aged man, and the accused, a scared-looking girl with a baby in her arms.

Ibn Shaprut sat silently at Ibrahim’s side, plucking at his shabby robes. The doctor was a big man who had been a lot bigger before this dreadful summer of siege. Now his grimy, much-patched clothes didn’t fit him properly, and Ibrahim sometimes thought his very skin hung loose, drained of fat. However Ibrahim was glad of his steady company and hard-headed advice.

It was an August afternoon in Seville, a city under siege and hot as a furnace. Distantly the muezzins called for prayer. Ibrahim was too busy for prayers. He tried to concentrate on the case.

The accuser was a man called Ali Gurdu. Aged about fifty, his face round as the moon, he looked sleek and prosperous in the middle of a famine that even reached inside the emir’s palace, though in August’s heat sweat stained his turban a grimy yellow. This man looked suspiciously at Ibn Shaprut. ‘Who’s he? A lawyer, a magistrate?’

‘I’m a doctor,’ said Ibn Shaprut.