'So pray for the souls of the dead children, friar. But remember that the Pope himself says that a war for Christ is a just war, however it's fought. And pray that you're never on the losing side.'

She was a hard, brutal woman. And though she must be near fifty now, the angry lust she had so carelessly stirred in him still flickered. She had made a peculiar enemy of him by the way she had treated him, he thought. He tried to conceal this from her. And he tried to dismiss from his own mind the thoughts he had of her, fantasies of lust and violence, in which he ended her domination of him once and for all.

After days on the road, they arrived at Ronda.

The port of Malaga was the Christians' next strategic objective, as it had been for two years, but its twin fortresses stood strong and stubborn under the command of the formidable El Zagal, and the Christians did not yet have the resources to deal with it. So they had focused their energies on destroying this town, Ronda, thirty miles inland and sixty miles west of Malaga, the key to the western defence of the residual Moorish state.

The site was extraordinary. Ronda sat on top of a butte, a pillar of rock. To the north was a steep-walled gorge. To the south the butte was lower, and here the Moors had built a massive fortification, a curtain wall studded by towers. The only way into the town was by a bridge that spanned the gorge to the north. James, studying this place, thought it was a textbook example of a natural fortress, a definition of impregnability. No wonder the Romans, those great military technicians, had settled here.

But the monarchs of Spain were here to take it, and the siege was laid.

The Christian camp, out of range of the Moorish defenders' cannons, arquebuses and crossbows, was a morass of mud and tents and stinking cesspits, over which a loose cloud of greasy smoke hung day and night. But as they approached, James saw with a helpless thrill that the banners of the monarchs hung over the camp. Fernando and Isabel, the modem champions of Christendom, really were here in person, not half a mile from where James and Grace pitched their own rough leather tent.

But this place of war was not comfortable.

When night fell great cannon began to roar. On the south side of the city, targeting the walls and towers, Fernando had drawn up a battery of immense new Italian guns called bombards. Their unceasing thunder was overwhelming, and the night was a hellish scene of half-naked men, blistered from the heat of the weapons, labouring amid a stink of gunpowder and smoke to load, aim and fire, over and over, the shot gradually battering down the city walls.

And as the day broke the Moors attacked – but they came from the hills, not from the city. James learned that these were the forces of the governor of Ronda. An experienced general called Hamet el Zegri, he had allowed himself to be lured out of his city to raid Christian fields and barns, a revenge for the chevauchee of his countryside. But the Christians had sent a cavalry detachment to cut him off from Ronda, and when el Zegri returned he found his town already besieged.

Still, under el Zegri's command the Moors came riding down from their hills, every day. The armies closed amid a roar of cannon and the popping of arquebuses and a clamour of war drums, and to cries of 'For Saint James!' and 'Allah akbar!' When the Christians mounted attacks, the Moorish would kneel in blocks, their pikes at the ready, soaking up the charges, their javelins in quivers to be flung with deadly skill. And the Moorish cavalry, lightly armoured, riding fast under their colourful battle flags, was much more mobile than the Christian knights in their heavier chain-mail and plate.

For all the bustle and excitement of the cavalry charges and the spectacle of the cannon and arquebuses, the real work of killing was done, as it had always been, with pikes and swords and scimitars, wielded by human muscle, one man against another. James was appalled by the utter, fully committed violence of these encounters, even though none of them was conclusive. Isabel had set aside tents to serve as hospitals, but they were overrun, and if you went to that part of the camp the groans of the dying and the stink of rotting flesh were unbearable.

For four nights the bombardment continued, and for four days the Moors attacked. James didn't sleep for a single hour. It was a time of utter misery, for besieged and besiegers. In the Christian camp, the supply lines to Cordoba were fragile, and all there was to eat was a disgusting mixture of flour in pork fat.

Relief came when the last of Ronda's towers was demolished, and the walls crumbled. James stood beside the silent bombards, watching the end game of the siege as the caballeros swarmed into the city, and the screams began.

A week after the Moors' capitulation, James and Grace were able to enter Ronda.

Walking in from the Christian army camp they passed a complex of buildings, arched roofs and domes, sheltering in the lee of the smashed city walls. It turned out to be a bathhouse; a marshy, steamy stink lingered in the air around it. The baths were working; on a squat tower the donkey patiently turned its wheel, watched by a Moorish boy with a switch, drawing up river-water to be fed via a slender aqueduct into the baths. Today the men who filed through its rooms were Christian soldiers, but the women who went with them were all Moorish. James wondered how many of them had a choice.

James and Grace made their way over the bridge across the gorge. The bridge was battered, but it had survived the bombardment. The gorge's walls loomed above them, and James peered up curiously. The limestone was cracked vertically and horizontally, heaped up in tremendous blocks as big as houses.

They clambered up steep cobbled paths into the city itself. Squeezed onto its table-top of rock and hemmed in by its walls, Ronda was cramped and crammed. The bombards' shot had created great splashes of shattered stone, as if immense raindrops had fallen from the sky. There was a prevailing stink of rot and raw sewage, even a week after the water supply had been restored. Soldiers worked, picking through the rubble, searching for bodies, pocketing anything worth stealing. No Moors were about. The soldiers said that everybody was either dead, fled or hiding.

With Grace leading the way they cut through the centre of the town, heading for the cliffs on the north-western side. The warren of streets was studded with fine houses, mosques and bazaars.

They came at last to the western boundary of the city, where the town simply came to an abrupt end, for the plateau on which it had been built fell away in columnar limestone cliffs. James looked down over a flood plain, a land of farms and orchards through which a river snaked lazily. It was all so far below him it was like staring down at a vast map. But much of the land was brown or black, the crops and trees burned out, and sluggish threads of smoke rose to pollute the heavy air.

And as he reached the very edge of the cliff James stepped into an updraught of warm air, blowing strongly from the ground below. Down there in the valley a breeze was blowing, but when it reached the vertical cliff face the moving air, with nowhere else to go, washed upwards in an unending invisible stream to ruffle the cloak of a curious English friar. For a heartbeat he was able to lose himself in simple wonder at this unexpected physical phenomenon, a fragment of the rich beauty of God's creation.

Then Grace plucked at his arm. 'Look,' she said. 'Haven't you heard the cheering? There she is…'

Reluctantly he turned, and immersed himself once more in the affairs of men.

A procession was approaching, advancing along the broad road that lined the cliff: gilded people, merchants and courtiers, senior military men dressed up like peacocks, a splash of Christian colour in this conquered Moorish town. Many of them had crusaders' crosses exquisitely stitched to their shoulders or breasts. There were some Moors in the group, grandly dressed themselves with their jewelled turbans glinting: the rich and powerful under the old regime, he supposed, now hoping to keep their wealth and influence under the town's change of ownership.