Navigator tt-3

by Stephen Baxter

  Ibrahim took a deep breath. 'I have no love of being buried alive. But it's my mother I'm more frightened of.'

  Peter laughed, and clapped him on the back. 'Come. Let's face our nightmares.'

  It turned out to be only a short walk, though a clumsy and difficult one, through the low tunnel. Ibrahim stumbled over a broken Roman tile. Then the tunnel opened out, and Ibrahim found himself walking into a big boxy room. Steps cut into the earth led down to a floor some distance beneath him. The walls were stone-clad, the ceiling timbered, and lamps glimmered in alcoves.

  And in this chamber, deep underground, machines brooded, dimly glimpsed. There was a great tube mounted on a carriage. An upright wheel turned, a treadmill, with a man inside it to work it. What looked like the skeletal form of a great bird's wing gleamed and creaked. Scholars and artisans moved among these creations, murmuring quietly.

  Ibrahim felt deeply uneasy, as if he had descended into a sorcerer's pit.

  Peter led him briskly forward. 'This was some kind of water tank,' he said in a murmur to match the subdued voices around them. 'Always built big, those Romans, even when it came to their plumbing!'

  'I never knew this place was here.'

  'Not many do. It's on no plans; I dare say your emirate doesn't know it exists. When we needed a place to work in secret your mother, ever resourceful, started asking around among the criminal element.'

  'Criminal?'

  'Smugglers. Hoarders. Even bandits. They knew of this hole in the ground. It wasn't hard to take it over, clean it up, extend it a little…'

  'Ah, the vizier's advisor. How good of you to make time in your busy schedule to visit your mother.'

  Ibrahim had not seen his mother for four years. Subh wore a robe, white and pristine despite the dirt, and her hair was piled elaborately on her head, jet black. Unlike Peter she showed not a trace of the passage of time; she was as upright, powerful and magnificent as ever. Peter seemed to cower before her; he was as much in her thrall as ever.

  Ibrahim bent forward to embrace his Mother.

  But she subtly moved back and offered her hand, cold, the palm oily. 'Let's keep things formal,' she said. She showed not a trace of emotion.

  'Mother, you haven't changed.'

  'And what of you?' she asked. 'You're clean enough. A smart costume. And well fed, it seems to me.'

  'I take only my ration,' he said stiffly, and it was true, though there were many in the palace who did not.

  She prodded his belly. 'In that case you're not getting enough exercise.'

  'What are you doing here, Mother?'

  'You know very well. Building the war engines that might save Seville. Walk with me. See what we have made…'

  She showed him her marvels. Here was a metal tube that used compressed steam to spit iron balls. Peter called it the 'thunder-mouth', for the great roar it would make when it was fired. Around the perimeter of the treadmill he had noticed was a series of crossbows. An archer sat at the axle, and as the wheel turned one bow after another was brought before him.

  'The archer only has to aim and fire,' Peter explained. 'See, the ingenuity is that the mechanisms of the wheel-engine load each bow for him as it turns. So this enables a much faster rate of fire than a conventional bow, without a loss of accuracy.'

  There were many such gadgets, most only half-finished, betraying ingenuity but fragility.

  Ibrahim refused to be impressed. 'This is all you've achieved, in five years?'

  Subh watched him gravely. 'Don't you think anything of our efforts?'

  He walked around the workshop. 'Your rapid-firing crossbow machine is vulnerable. A stick poked into the mechanism would jam it.'

  Peter said, 'But a row of these machines, fixed to the city walls when the Christians come-'

  'They would still break down. Men would do better.' He came to the thunder-mouth. 'This is more promising. More compact than a catapult, perhaps. Faster to reload and reuse. But it does no more than a catapult would.' He glanced around. 'I see nothing here which would give one side an overwhelming advantage over the other.'

  Peter sighed. 'Well, you're right about that.'

  'What we need,' Subh said, 'is Incendium Dei.'

  'Your mysterious Fire of God.'

  'Precisely. The fire that would turn these delicate gadgets into thunderbolts.'

  'But you don't have it,' Ibrahim said.

  'Joan of the Outremer never replied to my letter. And I regret writing to her now, for I told her something of what we have, without learning anything of her. I fear she might become a rival, not an ally.'

  'Actually,' Peter said, 'it's not just God's Fire we need, Ibrahim. For these engines to be realised fully we need the original designs.'

  'Ah,' Ibrahim said. 'The Codex. The treasure said to be buried under the floor of the great mosque of Seville. Is that why you asked me here? To get me to dig up the mosque?'

  'No,' Peter said. 'I invited you here, frankly, because I thought you should be reconciled with your mother.'

  'But now that you are here,' Subh said slyly, 'why not? You have the ear of the vizier. If you dropped a word-'

  Ibrahim shook his head. 'You have buried yourself in this hole in the ground for too long. Think what the mood is like outside! In this crowded city the faithful wash around the muezzin tower like a sea. If I were to order the mosque floor to be dug up, in the hope of finding plans for super-weapons, I would cause a riot. And besides the imams would never give permission.'

  'So you turn your back on us again,' Subh said, her tone poisonous.

  'I regret what has happened,' he said. 'Nothing should come between mother and son.'

  Subh said, 'But you still think I'm wasting my time down here, don't you? You're just as headstrong and unimaginative as you were as a boy.'

  'Yes. I still believe you're wasting your time. And so, it seems, am I.' He turned to leave.

  'If you won't help us,' his mother called after him, 'at least don't betray us. Don't let the emir put a stop to our work. Trust me that much.'

  He paused. Then, without looking back, he made for the tunnel that led to the air, and the light.

  XX

  Saladin found London overwhelming, after three years away. When he arrived with Thomas early one morning, the city was blanketed by fog, thick, dense, yellow, stinking. People went around with candles in their hands and bits of moistened cloth held to their faces. Even by the river it was no better, and the ships crept cautiously along, lamps strapped to their prows.

  Thomas Busshe led him to the abbey at Westminster, and they waited in a small room where a nervous young novice served them warmed wine. This was a room used by Roger Bacon, this brilliant monk of Thomas's, and Saladin leafed idly through a heap of the scholar's well-read books: a grammar by Donatus, the Consolation of Philosophy by somebody called Boethius, Aristotle's logics and metaphysics, with commentaries by later authors – even by an Arab. So many books, Saladin thought. Did the world need them all?

  The novice returned and said they had to wait for Bacon.

  'For, I'm told,' said Joan, sweeping into the room, 'today's the day for his annual bath, and he's not about to miss that for a couple of ragged refugees from the Outremer.' She was dressed smartly, in a long crimson robe and a white wimple.

  Saladin got to his feet and kissed his mother. 'You don't look ragged to me, Mother,' he said.

  'Appearance is everything.' She nodded stiffly. 'I thank you for the stipend you send me. I spend it well, I hope.'

  'Spend it as you like.'

  Her movements as she chose a chair and took her wine were firm and decisive. Her face was still young, he thought, still beautiful; she was only thirty-five years old. She was flushed, though, but not with health. Flushed with an impatience that had been building all the long years of her exile in England, as she saw it. She eyed her son. 'No wife yet? No grandchildren for me?'

  'Not since I last saw you at Christmas,' he said drily. 'And no husband for you, Mother?'
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  'A husband would only get in the way.'

  'He might provide you with an income,' Thomas pointed out.

  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,