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by Baxter, Stephen

  Joan snorted. ‘An income pledged to his ambitions, not mine. I’ve no use for that.’

  Thomas looked at them both. ‘You are mother and son, but so different. Saladin is finding contentment. He lives simply; he uses the skills God has given him; slowly, patiently, he is building himself a place in this country. He asks nothing, and he resents nothing. But you, madam, are full of anger, aren’t you? Rage, even.’

  ‘Rage?’ Her cheeks coloured, her eyes glittered, and her lips were thin. ‘If you say so. You men of the cloth are so terribly wise.’

  ‘But, Mother,’ Saladin said, ‘what are you angry about?’

  ‘What do you think?’ she flared. ‘This is not my country. I despise the weakness of these Christians of the west, who cannot, it seems, summon the will to take back the lands which were lost - our home, Saladin. I have no wealth, no position. I am not respected here. Though my ancestors fought and died to win the Holy Land for Christendom, the people in this country even mock the way I speak. Can they not see who I am - what I am?’

  Saladin was saddened. ‘And is this why you want to build your engines? To change the way people look at you?’

  She stared him down.

  But if this was true, Saladin saw with dismay, then his mother had no choice but to pursue her dream of engines of war; the logic of her personality dictated it. And, Saladin sensed with dread, he was destined to follow her.

  The door crashed open. They all flinched.

  A monk burst in, tall, skinny, agitated, and with his tonsured hair comically sticking up around his bald pate. He looked younger than thirty. ‘Thomas!’ he shouted without preamble. ‘Good to see you again. And this must be Joan of Jerusalem, and her son, fascinating, fascinating, you who brought the conundrum of time to my door, you who believe past and future are all muddled up.’

  Thomas said, ‘Roger—’

  The man dumped a leather folder on a low table, and kept talking. ‘And why should time not be mixed up? All is in flux, the world is an unstable place. Heraclitus pointed out that he was never able to dunk his foot in the same river twice, for it changes with every instant - you see? So why, then, should we imagine that even the river of time is inviolable and unchanging? Perhaps it is more like the fabled Meander in Phrygia, which changes its course with every season, endlessly seeking the perfection of its Platonic ideal. So, then, perhaps history is made and remade, cutting through our lives as a wandering river cuts through sandbanks, for ever seeking some new and more perfect shape. Why not, I say, why not? Shall we get to work?’

  Joan turned to Thomas. ‘Who is this person?’

  ‘One of the liveliest minds of this new age of scholarship, that’s who,’ said Thomas.

  ‘One of ...’

  ‘Which is why I took your puzzle to him. Joan, Saladin, this is Roger Bacon, born in Ilchester, trained in Oxford, and now lecturing in Westminster.’

  ‘Don’t forget Paris,’ Bacon put in.

  ‘I have been aware of his career since his student days - oh, a decade back now. You studied the classics at Oxford, did you not, Roger?’

  ‘And geometry, arithmetic, music, astronomy. I worked under Robert Grosseteste.’

  ‘The bishop of Lincoln—’

  ‘Who has led the reintroduction of the works of the Greeks into England.’

  ‘Roger lectured in Paris—’

  ‘I earned my master of arts degree there. I saw Alexander of Hales there, and twice saw William of Auvergne dispute...’

  This fast-paced duologue was hugely confusing to Saladin, who had heard of none of these scholars.

  ‘I see myself now as a dominus experimentorum,’ Bacon said.

  Joan glanced at Thomas. ‘What does that mean?’

  ‘One who studies the physical world,’ Thomas said, ‘and tinkers with it, in the hope of learning more about the truths of God.’

  ‘I have always “tinkered”,’ Bacon said. ‘I once set up a candle and a mirror in a darkened room, and peered into the eye of a cat. Have you ever tried such a thing, brother Saladin?’

  ‘I can’t say I have.’

  ‘You see a carpet of dusky red vessels overlaid by a golden tracery. Quite beautiful, quite mysterious. My study in optics began with those first observations. And if you could look into the head of a man, what would you find? But I have never been able to persuade anybody to sit still long enough to let me see. Ah, well.’

  ‘I thought all truth was to be found in the Bible.’

  ‘Of course, and in the authorities of antiquity. I myself am one of Europe’s leading scholars on Aristotle,’ Bacon said without a shred of modesty. ‘But there are many routes to the same destination, which is God’s truth. The role of the natural philosopher is to understand how phenomena reveal that truth. Saint Augustine himself instructed us not to embarrass ourselves by quoting the word of God to contradict some fact of nature, because that would only reveal that we understood neither the word nor the nature. Experimentation: that is the way to that deeper truth, that final reconciliation. Or so I am coming to believe. Perhaps you have heard of the work of Master Peter de Maricourt, a Picard who once took the Cross, and subsequently—’

  ‘Yes, yes, Roger,’ Thomas cut in. ‘But perhaps we should get to the point?’

  Bacon smiled, utterly in control. ‘Quite right, Father, quite right. You!’ He jabbed a finger at the novice, who jumped. ‘More wine for our guests. And bring a lamp over here.’ He sat before the low table, opened his leather wallet and extracted papers that he proceeded to spread out. ‘We have a deep mystery to unravel.’

  Saladin murmured to Thomas, ‘He’s quite a showman, isn’t he?’

  ‘And he knows it. But it’s not necessarily good for him. Ah, Roger, Roger, how your busy head distracts your pious heart!’

  But they sat before Roger Bacon, wide-eyed, as he began to reveal the truth of the Incendium Dei cipher.

  XXI

  ‘We begin with your fragment of coded text, as Thomas presented it to me,’ Bacon said. He spread out a parchment on the table:

  BMQVK XESEF EBZKM BMHSM BGNSD DYEED OSMEM HPTVZ

  HESZS ZHVH

  ‘I was intrigued by the puzzle...’

  ‘I knew he would be,’ Thomas whispered to Joan. ‘Very useful thing about scholars, that curiosity. He didn’t even ask for a fee.’

  Bacon glanced at Saladin. ‘You. Tell me what you see.’

  ‘I’m no scholar—’

  ‘Just answer.’

  ‘I see ten words,’ Saladin said. ‘Latin letters, not Arabic. I recognise none of the words, though.’

  ‘And nor should you, for they aren’t words at all. Even these groupings are a decoy, I quickly realised. This is no sentence. Look at them! What sentence has words of such regular lengths?’

  ‘It is written in a cipher,’ said Joan. ‘That much is obvious.’

  ‘Yes! But what cipher? What do we known about ciphers? You, Thomas?’

  ‘Just get on with it, Roger.’

  ‘Oh, very well. The first cipher was used by the Spartans, long before the birth of Christ. They had a device called a scytale. You would wrap a strip of leather around a baton, and write out your message; once unwrapped the letters are scrambled, you see, illegible to anyone who doesn’t have a baton of the same dimensions. Tacitus wrote of codes and ciphers, as did the Greek Polybius. Julius Caesar used a substitution cipher, which depended on a simple cyclic displacement of the alphabet. Caesar used a displacement of three positions, while Augustus later used one.’

  ‘I’ll be the one to ask,’ Joan said heavily. ‘What is a “simple cyclic displacement”?’

  Bacon reached for a bit of chalk and scribbled on the tabletop. ‘You write out your alphabet. A, B, C, D. And you write it out again with the letters shifted through three spaces, say. D, E, F, G. You have the word you wish to encode, say “CAESAR”. And you exchange the true letters for the shifted ones. So C becomes F, A is D, E is H ...’

  ‘I understand,’ said Joan.


  ‘Now, history tells us there have been ciphers a good deal more sophisticated than that. Polybius himself described a bilateral substitution system, which means... never mind! Happily for your weary brains, I soon concluded we aren’t dealing with anything much more complex than Caesar’s substitutions.’

  ‘Why do you believe that?’ Saladin asked.

  ‘This is a message in the Latin alphabet, not Arabic or Persian or Greek. So it is surely a Latin message. The Moors of Spain are developing extremely advanced cryptographic systems, I’m told. But a thousand years after the Caesars, we Latin scholars still lag behind the rest in our ciphers as in everything else. One point on which I kept an open mind was which alphabet we are using here.’

  ‘The Latin one,’ said Saladin.

  ‘Ah, but which Latin? Caesar used twenty-three letters. We use twenty-five, for we have added U and J. I thought it most likely the classic alphabet was the one employed.

  ‘So I began my analysis. A common technique in breaking ciphers is to study the distribution of letters. The most common symbol is likely to correspond to a common letter in plain language - E perhaps, or S, or T. But this fragment is too short to enable such a count. I experimented with scytales of various dimensions, to no avail. And I tried all the possible cyclic permutations, with no luck either. With all the permutations exhausted, I racked my brains for a new way forward.’

  Joan murmured, ‘And in the end, after much heroic struggle, you found a way, did you?’

  Bacon blithely ignored her sarcasm. ‘A simple variant on cyclic substitution is to use a key.’

  ‘A key?’ Saladin asked.

  ‘Caesar, for instance, could have used his own name.’ He wrote it out: CAESAR. ‘We must eliminate repetitions.’ He crossed out the second A. ‘Now we use this five-letter key as the foundation of our cipher.’ He wrote out a twenty-three Latin letter alphabet with a code beneath it:

  ‘You see? A substitution with the shift depending on the key word, and with those letters removed. So the word CAESAR now encodes as—’ He wrote it out:

  ECRQCP

  ‘It’s a poor sort of code,’ Saladin observed. ‘The last few letters are transcribed without change.’

  ‘You’re a practical man, I can see that,’ Bacon said. ‘That’s true. But there are easy variants. The simplest is to put the key word at the end of the alphabet, not the beginning, and to proceed backwards.’ He scribbled quickly,

  ‘Now all the letters save one have a different symbol.’

  ‘This is all very well,’ Joan said, ‘but we don’t have a key, do we?’

  ‘Oh, but we do,’ Bacon said. ‘You gave it to me - or rather, to Thomas.’

  ‘I did? What key?’

  ‘It was in the letter you received. From your cousin in Spain. The phrase she was particularly interested in, that appeared to be left incomplete on the scrap of parchment you held.’

  ‘Incendium Dei,’ Saladin said, wide-eyed.

  Joan stared at Bacon. ‘Can it really be as simple as that?’

  Bacon grinned. He now had a full hold on their attention, Saladin thought, and he knew it. ‘Shall we try it?’ He wiped the table clean of chalk with his sleeve, and began to scribble again. The three of them bent over to see. ‘We begin with the key,’ Bacon said. He wrote,

  INCENDIVM DEI

  ‘The U replaced by V as you see. Next we eliminate duplicates.’

  INCEDVM

  ‘There is our key. So we construct our code. I tried out a forward substitution, but succeeded with a backward...’ He scribbled rapidly.

  ‘Now we reconstruct our message. That first B becomes a P, the M becomes R ...’

  BMQVK XESEF EBZKM BMHSM BGNSD DYEED OSMEM HPTVZ

  HESZS ZHVH

  PRGSL CVEVO VPALR PRMER PNYET TBVVT IERVR MHDSA

  MVEAE AMSM

  Saladin stared at the new string, unreasonably disappointed. ‘It’s still nonsense.’

  Bacon smiled, a magician with another trick to show. ‘A simple transposition would be too easy. Our puzzle involves numbers as well as letters. Look at the “sentence” again. Nine “words” of five letters, and one of four. What sentence is as regular as that? What we have here is a simple string of letters, of length - how many, Thomas?’

  ‘I’m not one of your Parisian students,’ Thomas growled.

  ‘Just answer,’ Joan murmured.

  ‘Forty-nine, then.’

  ‘Good. What’s significant about the number forty-nine?’

  ‘Seven sevens,’ said Saladin immediately.

  ‘Very good!’ said Bacon.

  Thomas looked surprised. Saladin said, ‘Some of the villagers think it’s a lucky number. Seven times seven. That’s how I know.’

  ‘Seven squared,’ Bacon said. ‘That is surely a clue. So now, if we write out the decoded message again, not in these arbitrary blocks of five or four, but in a grid of seven by seven...’

  ‘It still means nothing to me,’ Joan said.

  But Thomas was tracing the letters with a chalky fingertip. ‘But if you read, not across, but down - else why put them in a grid at all? P - E - R ... Give me that chalk, Roger.’ He wrote out the letters, column by column, as a single line.

  PERNVMERVPYTHAGOREIDESVMTESALPETRAMCARBVM

  SVLPVRVM

  ‘Look at this string,’ Thomas said, excited. ‘Pythagorei - see it? Surely there is meaning here at last.’

  ‘Good, good,’ Bacon said. ‘You can imagine the variants I explored before I hit on this correct route through the maze. Now all we have to do is find the breaks between the words...’

  But Thomas was ahead of him, splitting the line with bold slashes.

  PER / NVMERV / PYTHAGOREI / DESVMTE / SALPETRAM /

  CARBVM / SVLPVRVM

  And there, for Saladin, the magic happened, a readable sentence emerging from a clamour of nonsense. He was the first to read it aloud: ‘“By Pythagoras’s number take saltpetre, charcoal, sulphur.”’

  ‘Almost there,’ said Bacon. ‘Almost there.’

  ‘But what does it mean?’Joan said.

  ‘Well, Pythagoras’s number is obvious. It is six.’

  ‘It is?’

  ‘Six is the perfect number,’ said Saladin.

  Thomas raised his eyebrows at him. ‘And why is it perfect?’

  ‘Because if you take the numbers that divide into it evenly...’ Saladin took the chalk now, and wrote out, 1,2,3. ‘If you add them up you get six again.’ 1+2+3=6.

  Bacon smiled. ‘Once again you surprise us.’

  Saladin felt sheepish. ‘Another lucky number for the villagers.’

  ‘In fact there are many perfect numbers,’ Bacon said. ‘Pythagoras did indeed study them. Twenty-eight is the next one. You see, it is divisible by-’

  ‘Never mind,’ Joan said hastily. ‘So now we have this: “By one, two, three take saltpetre, charcoal, sulphur.”’

  ‘Or,’ Bacon said, ‘three, two, one. In fact those proportions aren’t quite correct, but near enough the range that a little trial and error gives you the right product. The value of experimentation,’ he said, smiling.

  Saladin was mystified again. ‘What product?’

  ‘Why, it’s obvious - black powder. Haven’t you heard of it? The Chinese have studied it for centuries, we’re told. They call it the “fire drug”. It’s said they found it looking for an elixir of life! I had been hoping to obtain samples via the trade routes opened up by the Mongol empire, in order to verify its properties for myself. Now I can begin to experiment with its very manufacture.’

  ‘The manufacture of what?’ Joan demanded. ‘What does this stuff do, you infuriating monk?’

  He didn’t seem insulted. ‘Well, if you set fire to it—’

  ‘Yes?’

  ‘It explodes.’

  XXII

  They sat around the low table, heaped with Bacon’s papers and covered with chalk scribbles.

  ‘Explodes,’ Joan said.

  ‘Someb
ody,’ Bacon said, ‘your Weaver of the tapestry of time, Thomas, wants you to make explosions. Incendium Dei indeed. I wonder why.’

  Joan glanced at Thomas. ‘Have you told him of the engines?’

  Thomas closed his eyes. ‘No. Because I did not have your permission. And because, frankly, I was frightened where it might lead, if he knew.’

  Bacon’s eyes were wide. ‘What engines? You must tell me.’

  Thomas glanced at Joan. ‘You see what I mean?’

  Joan said, ‘Well, we are committed. And perhaps this strange monk of yours can help us.’ She described succinctly the legend of Sihtric and his machines of war, the plans now believed lost beneath the floor of the great mosque of Seville, in faraway al-Andalus.

  ‘But you must retrieve this Codex,’ Bacon said. ‘You must!’

  ‘Why?’

  ‘Can’t you see? Combine these engines of war, engines that roll and swim and even fly, with the black powder, with the Fire of God, and no man could stand before you. Think of it - a miniature Vesuvius loaded on each arrow! ...’

  Saladin’s experience of explosions was limited. But once he had seen a forge blow itself apart. He tried to imagine such energies harnessed, launched, and used against the flesh of enemies.

  ‘He’s right,’ he said reluctantly. ‘You told us, Thomas, that Sihtric was dissatisfied with the engines he made. Perhaps this black powder will provide the potency they always lacked.’

  Thomas looked pale. ‘If it can be made to work - but what a horrible vision of destruction! What man is this Weaver to scatter the seeds of such carnage in our age?’

  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.’