When the caliphate fell, al-Andalus splintered into taifas – so many of these little statelets that nobody had been able to count them; there may have been three dozen. But as is the way of politics and war the taifas had squabbled among themselves like fish in a pond, eating each other up until there were only half a dozen left.

As they drove steadily south the land became ever starker, drier, dustier, baked in the heat. And yet the irrigation channels brought green life to the land in great broad strips. Sihtric said that 'water courts' sitting in the towns supervised the upkeep of the irrigation systems, which were a communal treasure. The land actually seemed richer than England, where the peasants toiled with heavy ploughs. But then this land was not as God had designed it but as people had made it, people who had walked out of deserts, who knew how to extract life from the slightest drop of moisture.

In one place where they stopped for the night, Marwam paid a farmer a few coins for them to pitch their blankets under the shade of fruit trees. Robert had never seen such fruit, heavy and bright. They were oranges, Moraima told him, an Arabic name for a fruit brought here by the Moors. She clambered up a trunk and picked a couple of samples, and showed him how to remove the thick peel. When he dug in his thumbs he squirted her with zest, and when he bit into the fat segments, juice gushed out and rolled down his chin. The orange was bitter, making his tongue curl, but the flavour was like light in his mouth.

So they ate their oranges, their faces plastered with sticky juice and zest, laughing at each other. It was a simple, wordless moment between the two of them which even the faithless camel driver couldn't spoil.

V

At last the party came to Cordoba.

Approaching the walled kernel of the city, they passed through a hinterland of cultivated country. Farthest out estates sprawled, astonishingly green, with hanging gardens and citrus groves crowding the river banks, and with buildings like blocky jewels shining in the sun. These estates were like the villas of the long-gone Romans, Sihtric said. He called them munyas, country houses.

Then the old roads brought them through suburbs of the city itself, communities of mud-brick houses that jostled by the road. Sihtric said that the city had long outgrown its Roman walls, and many of its necessary functions had been transplanted out here: residential areas, markets, bathhouses, industry, gardens. Most of the buildings inside the city walls were official, such as palaces, a chancery, the mints, prisons.

But the place had seen better days. The travellers passed burned-out buildings, and even some grand estates looked abandoned. These wrecks were nothing to do with the Christian armies but were scars of the wars between Muslims. Cordoba was no longer a capital of anything, not even of its own destiny, for it had been absorbed into the rule of a taifa run out of another Moorish city called Seville.

As they neared the city, vendors of water sacks, meat on sticks, and even bits of sparkling jewellery crowded around the travellers. Beggars too pushed forward, holding up the stumps of severed arms, or stretching open hideous wounds on their faces. Old soldiers, perhaps, or refugees from the cities the Christians had occupied to the north.

At last Cordoba itself loomed before them, a walled forest of minarets and domes and cupolas. They approached a gate in the walls, one of seven. Traffic streamed through it, pedestrians, horses, mules, the camels towering over the rest.

Soldiers stood by the gate, languid. Robert studied them. They wore quilted jackets over long mail coats, and round helmets, and they had mail masks they could pull up over their faces. They carried shields of wood, long spears, stabbing swords and complicated-looking bows. Some of them carried crossbows, which Ibn Hafsun said were of a design that dated back to the Romans. It seemed odd to Robert to see a soldier without Christ's cross emblazoned anywhere on his costume.

They lodged their animals at a stable, and left instructions for their goods to be brought after them. Robert was surprised to find slaves working here; there weren't many slaves in England.

Then they walked into the crowded city itself, Sihtric leading the way. The streets were so narrow that in places two people couldn't pass without brushing, and woven into a network of dead ends and double-backs so dense that Robert was soon lost. His nose was filled with the spicy scents of unfamiliar cooking, and his ears rang with the muezzin cries that billowed out from the towers of the city mosques. Marwam had already turned back, to Robert's relief, but the faces crowding around him were like a hundred Marwams, dark, sharp, their alien language studded with bits of Latin.

They passed an arched gateway in a wall, lobed, delicately shaped of soft stone and covered with intricate carvings. Robert's gaze was led through the arch from the shadow of the street into a sunlit courtyard, where a fountain bubbled in a square garden of tiles and green plants. There was nothing like this in Robert's England, a place of gloomy fortified towns and brooding Norman keeps, nothing like this garden full of water and sunlight. It was like looking through a hole in the wall of the world, a glimpse of paradise.

'This is how we do things here,' Moraima said, watching him. 'Our gardens are the hearts of our homes. Our wealth, poured into beauty for those whom we love to enjoy. Is it different where you live?'

He saw the light of the secret garden reflected in her deep eyes, as if they too were doorways he might enter.

Ibn Hafsun nudged Orm and sniggered, and the girl laughed, and the moment was lost.

They spent a day resting.

Robert, unable to sleep late for the heat, was up at dawn. He went walking at random.

The city was awake before he was, the streets bustling, the markets and mosques busy in the blue-grey light, the muleteers driving their beasts out of the city gates. As he walked he gradually got used to the layout of streets. Moorish houses were knots of buildings gathered around a courtyard, to be reached by narrowing paths that budded off wider highways. There was a logic to it, but it wasn't the straight-line logic of a Roman city like London; here the streets branched like the limbs of a tree, leading to endless dead-ends. The people weren't like English people either. They were a mixed-up sort, the result of generations of intermarriage between the invaders and the old Gothic peoples. Not everybody was Muslim either; there were Christians here, and many Jews.

The city nestled within the circling safety of its old Roman walls, which ran down to a river where waterwheels turned languidly, and which was still spanned by a stout Roman bridge. The city's heart was full of grand buildings, finely tiled, intricately adorned with carved stone and moulded plaster. The greatest building of all was a vast mosque that sprawled in its own compound close to the river: a temple to a god who was not God, a firm Islamic statement planted proudly in a Roman city. There was a sense of wealth here, Robert thought, of care, of intensive labour over every detail. And yet it was an architecture born of war. The buildings had stout fortress-like walls and towers and gateways, but these warlike structures were made elegant by their proportions, and the fine embellishment of fretwork and stucco and inscription.

As the day wore on he learned the cycle of the city. Because of the heat and the light the very rhythm of life here was quite different from any English city. As noon approached the people retreated to the shade of their homes, windows closed and shutters drawn. Even the animals grew quiet, as if the whole city slept beneath a shroud of dense, dusty orange air. But as evening approached and the first whispers of coolness arrived, the city began to stir once more. The street lights were lit, and the city came alive as a firmament of light and movement, of music and laughter.