And the people of the marshes were only dimly aware of what was going on outside their watery realm. As the King's procession passed, one grubby old chap had called, 'What's up, are the Romans back?'

Despite the sanctuary of Aethelingaig the flight from Cippanhamm was an utter humiliation, made worse by the fact that the King's own estate had been taken by the Danes as a base. The very boldness of the Vikings' strike was daunting, Cynewulf thought. Guthrum's intention had clearly been to capture or kill Alfred himself. If he had done so, with only children available to occupy the last English throne, Wessex could have been thrown into a succession dispute and fratricidal turmoil – and with a single stroke Guthrum might have won England. The intelligence of the attack, its decisiveness, and the wile with which it had been carried out marked out Guthrum as a formidable leader.

And worse in Cynewulf's mind was the vision of Egil son of Egil, the Beast from the outer dark who had rampaged through the broken sanctuary of the King's hall.

'Yet they failed,' Arngrim had pointed out to Cynewulf as they discussed this. 'There is still hope.'

But Alfred could not fight back, not for now; English farmer-armies could not be raised in the depths of winter.

By the time Arngrim and his companions got back to Aethelingaig after their spying expedition, Alfred's men had had three days to get organised. Around the camp a ditch had been dug out and an earthen bank thrown up. Inside this perimeter turf fires burned smokily, tents had been set up, and latrines and food pits were being dug. Parties had been sent out into the countryside to demand food for the King from the soggy water-folk. Further afield rivers had been blocked with logs to keep the Danes from sailing up.

This toy fortress, scratched out of a sodden moor under a sky like a grey lid, was all that was left of the domain of the King of Wessex.

In the camp the thegns huddled in uneasy groups, poring over bits of parchment, some even scribbling maps in the mud with bits of stick. The King was nowhere to be seen. Arngrim quizzed the thegns, telling what he had learned himself and finding out what else was known.

The news was detailed, surprisingly, since even here the King's clerks scribbled and jotted constantly. After nearly a century of the Viking catastrophe the monastic system had collapsed and England was left empty of scholars. It was a tragedy for a land that in Bede's time had been full of books and learning. But to Alfred, the scholar-King, words on parchment were a weapon of war; he knew that it was with words, words, words, endlessly recorded, that the Roman army had mustered the deep collective wisdom that had once enabled it to conquer the world. So Alfred had searched for literate servants from the British nations of the west and north, from Ireland, even from the continent.

Today the news, however painstakingly assembled, was dismal.

There were three principal nations among the Northmen: the Norse, the Swedes and the Danes. It had been the Norse who had first struck at Lindisfarena. They assaulted Britain, Ireland and the Frankish kingdoms. Colonies were planted in Ireland, and on Britain's offshore islands. Some said the Norse had pushed ever further west, seeking lands beyond the ocean known only to the ancients.

The Swedes, meanwhile, looked east. Using the great continental rivers, even dragging their boats between river courses, they plunged deep into Asia. In the end they had attacked even Constantinople.

And the Danes, said to be fleeing tyrannical kings, turned west and south, hitting Britain and western Europe. The petty kingdoms of England and a fragmented Europe had been ripe fruit to be plucked by these ferocious raiders. After five decades of pinprick assaults the character of the incursions changed. A new generation of Danish invaders came in great coordinated waves, far more numerous than before, and they began to overwinter. They had come to seize, not just wealth, but land.

Alfred's whole life had been shaped by the wars with the Danes.

All four of the sons of Alfred's father, Aethelwulf, became kings. And it was in the reign of the second son, Aethelbert, that the Danish Force came to England, a unified army of perhaps two thousand warriors. The Danes landed first in East Anglia, whose king sued for peace. Then they headed north into Northumbria, where as usual rival kings were at each other's throats. The Danes burned out the great old city of Eoforwic, and in a great bloodbath around the Roman walls both the rival Northumbrian kings were slain: one of them, Aelle, suffered the blood eagle, his back split open and his lungs splayed. Northumbria, a kingdom which had once dominated Britain, had collapsed like a dry mushroom.

In the next season the Force turned on Mercia. Alfred, still just nineteen, fought in a siege of the Danes at Snotingaham. Mercia fell; the Force took Lunden, among other prizes. The East Angles now made a belated stand, but their king, Edmund, too was toppled; he too suffered the blood eagle.

Just five years after the Force landed, only Wessex survived, and it bore the brunt of the Force's fury. Alfred and his brothers won one mighty victory for the English, at a place called Aescesdun. But the repeated battles proved inconclusive. King Aethelred, Alfred's last surviving brother, died of wounds incurred on too many battlefields. Alfred, succeeding to the throne, sued for peace; both sides were exhausted.

The Force used the time to consolidate its gains. More Danes flooded over from the homeland to settle in Northumbria, East Anglia and in the north-east of Mercia. Their leaders were already minting their own coins in Lunden, and Eoforwic began to develop as a Danish market town, a hub of a trading federation that stretched from Ireland across northern England and deep into Europe and Asia beyond.

The mass of the common folk toiled at their land as they had always done. But if Wessex fell it would be the end of England. And in a new Dane-land, determinedly pagan, thoroughly illiterate, Danish-speaking, the brilliant age of Bede would soon be but a dream.

The peace won by Alfred had been broken the previous year when the Danes, now under their petty king Guthrum, at last moved against Wessex. Storms wrecked their ships; weakened and cut off, Guthrum agreed another truce with Alfred, and withdrew. It was this truce which the Danes had treacherously broken, in their Twelve Days assault on Alfred's estate at Cippanhamm.

And now, Arngrim learned, the news was worse yet. Since Cippanhamm many of the Wessex nobility, losing faith in English kings, had thrown in their lot with the Danes.

When they had gleaned all they could from the dispirited thegns, Arngrim, Ibn Zuhr and Cynewulf found logs to sit on. Cradling mugs of bark tea, bitter-tasting but warming, they huddled in cloaks that were damp with dew, for the short January day was already ending.

Arngrim grumbled, 'The King skulks in his tent, attending his endless prayer services and having his meaningless thoughts copied down by his clerks. He isn't doing anything.'

'It's said he muses on the ageing of the English race,' Cynewulf said. Our centuries of vigour are done, and now we must be pushed aside, as once we pushed aside the Romans.'

Arngrim grunted. 'If you asks me he spends too much time thinking about the Romans.' Alfred's father Aethelwulf, deeply pious himself, had sent his youngest son to Rome, twice before his tenth birthday. Alfred was struck deeply by the ancient city, its fabric rotting after centuries of neglect and sackings. 'I heard a rumour that he's planning a pilgrimage to Rome. He wouldn't be the first to escape that way.'

'That,' said Cynewulf, 'would be a disaster.'

'Well, if the King is in shock, it seems to me he must be drawn out of it. But how?'