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.