'Not so high,' Robert said fiercely, 'that Alfonso's Christian armies could not drive the Moors out.'

Ibn Hafsun shrugged. 'Well, that's inarguable.'

'Must it be so?'

The soft voice startled Robert. It was Moraima, who had come to ride alongside the two of them. She spoke English, her father's language, but heavily accented.

Robert said to her, 'Those are the first words you have spoken to me. And must they be about war?'

'But it's all you talk about. You and our fathers.' Her voice, like her face, was delicate, and yet Robert thought he saw a strength beneath the fragile surface. It only made her more desirable.

'We weren't talking about war. Ibn Hafsun was telling me about the country.'

'Ah,' said Ibn Hafsun, 'but you are a warrior of God – a warrior cub at any rate. Tell me that you aren't dreaming of riding across this land in your mail coat, your sword in your hand, at the side of Rodrigo, El Cid, "The Boss", the greatest Castilian warrior of all!'

Moraima laughed, a sound like bubbling water. 'I ask you again, Robert: must it be so?'

Robert said reluctantly, 'The Pope himself says that if you fight to reclaim Christian lands from infidels, you are fighting for Christ.'

'Well, the Pope would say that,' Sihtric called back from his own mount. 'But the Pope has wider ambitions.'

Across Europe the conflict between Christianity and Islam was already four centuries old. Now the Seljuk Turks, ferociously warlike, had taken the Holy Land itself, all but extinguishing Christianity in the country that had given it birth. And they pressed on the East Roman Empire, long the bulwark between west and east, taking the rich province of Asia Minor. Alexius, emperor in Constantinople, had appealed to the west for help. But after centuries of invasions and war, the post-Roman states of west Europe were like armed camps, fractious and suspicious, bristling with petty armies any of which would have been dwarfed by the legionary forces of old. The Pope, spiritual leader of all these domains, longed to unify them in a great cause.

'And what better ambition for a pope than a war against Islam?' Ibn Hafsun murmured.

Moraima eyed Robert again. 'I ask you once more: Must it be so?'

Robert said, 'I hope not.'

'You do?'

'I would rather you and I were friends, than enemies.'

'Then we will have to see how this little adventure of ours unfolds, won't we?' And she trotted back to her father's side.

The older men exchanged bawdy glances, but Robert ignored them.

In the days that followed, as they pushed steadily south, the country became rougher. The olive groves and vineyards grew wild, the scrub encroached on the roads, and many of the towns looked abandoned. There were some inhabited communities, but all were heavily defended: fortified hilltops, towns with complicated systems of walls and towers. Ibn Hafsun and Orm kept their swords exposed.

Ibn Hafsun said, 'This is the boundary, Robert. This is what you get when great civilisations rub against each other. The Arabs have a word. They call this the tugur. The front teeth.'

At last they party approached Toledo. The party drew to a halt, all of them subdued.

It was mid-afternoon, and the sun was in the south, so that, approaching from the north, Robert saw the city in silhouette. The heart of Toledo was a fortress that sat on a promontory, with a river glistening at its feet. And on the plain outside the town, across a stout stone bridge, an army had gathered, pennants glittering in a cloud of dust, tents fluttering in the soft breeze. It was a Christian army, gathered under the cross of Jesus.

Ibn Hafsun came to Robert. 'What do you make of it, soldier?'

Robert glanced around. 'A naturally defensible site, on that rock. The river guards it on three sides. The walls are Moorish?'

'Roman, then Gothic, then Moorish.'

'And yet the town fell to Alfonso.'

'Only months ago. The wounds are raw. You have come to the very edge of Christendom, young soldier. We will stay here only one night. The city is a place of narrow streets, winding, many shadows. Watch your back, and your father's. And tomorrow – al-Andalus! Or what is left of it. Now, come. Have you any coin? I have a feeling those soldiers of the King will extract a toll from us for crossing their bridge…'

The next day, beyond Toledo, they pressed on, further south again. With every plodding step of the camels the heat gathered, and Robert Egilsson felt as if he was being walked steadily into some great hearth.

They were deep in the territory of the Moors now. That became apparent the first time they stopped at a small town to replace a lame camel. Marwam, a dark, skinny, rodent-faced man, insisted on replacing both their camels with fresh beasts, and for the price he threw in his own services as an escort.

'It might be wise,' said Ibn Hafsun. 'We're a long way past the border with the Christians, but relations are tense among the taifas – I mean, the Moorish kingdoms. You never know when you might cross the wrong border, or fail to pay the correct toll.'

But Sihtric snorted his contempt. 'Waste your money on this weasel-eyed camel-driver if you like. I'll have nothing to do with it.'

So Marwam joined the party. As they left, a gaggle of little children ran out onto the road to wave them off, shrieking and jumping, all of them as rodent-faced as Marwam.

Marwam was the first authentic Moor Robert had met – not a mixed-blood like Moraima, or a descendant of a Gothic Christian like Ibn Hafsun – and Robert watched him curiously. Dressed in swathes of grubby white cloth, Marwam was a wiry man who looked as at home on a camel as on foot. As they rode along he sang wailing, nasal songs, the songs of a desert people sung in a country that had once been Roman. But Robert thought that sometimes he was singing to Moraima, for he would gaze at her with deep brown eyes, his words sung in an unfamiliar tongue making Moraima blush.

Robert muttered to his father, 'If I knew the Moorish for "remember your wife and kids" I'd sing that back to him.'

Orm grinned, tolerant. 'I wouldn't worry. She's a city girl. I don't think she has any interest in camel-drivers. He's just flirting, and so is she. Besides, shouldn't you put such things out of your head? Jealousy is a Christian sin, I imagine. As is lust.'

'Most things are,' Robert conceded gloomily.

In all this business of borders and tolls and taifas, Robert was learning, to his surprise, that there was more than one Moorish country here in Spain. He had imagined that all of Islam would be united like one vast army, without individual faces or minds, under the orders of the caliph in Baghdad.

In fact the Muslims were diverse peoples. Even the armies who had originally invaded Gothic Spain three hundred years ago – whom the Christians called Moors, imagining they came from the old Roman province of Mauretania – had not all been Arabic. The leaders had been Arab, yes, but they had been outnumbered by their Berber warriors, who came from the harsh lands of the Maghrib just to the south across the Pillars of Hercules. Many of the Berbers' descendants were prone to complain, even fifteen or twenty generations later, how they had been tricked by the Arabs when it came to parcelling up the old Gothic kingdom.

And, Robert learned, Muslims went to war with each other, as well as with Christians.

It had been fifty years since a single ruler, in Cordoba, had controlled all the Muslim lands in Spain. That ruler, remarkably, had been a second caliph, independent of the one in faraway Baghdad. 'It is as if,' Sihtric said, 'a city like Paris or York hosted a second pope of its own.'