William first had to persuade his own counts to follow him. Few of them had even ventured across the ocean before. England was strong and formidably organised, and Harold was well known to be a competent general. An expedition against England would be orders of magnitude more difficult than an adventure against Maine or Brittany.

But if England was powerful it was also rich. And it was the wealth to be won in this gamble of a lifetime that seduced William’s warriors. One by one, strong-armed, cajoled and bribed by William, they came round.

Meanwhile William sent embassies to the Pope in Rome. In an elaborate scheme to seek the Pope’s backing for the war, William was able to point to Edward’s promise of the throne, and Harold’s own broken oath; Harold was a perjuring usurper. Not only that, he was portrayed as complicit in the crimes of his father, including the murder of Alfred, Edward’s older brother.

Orm the pagan had always thought that Christ was a prince of peace, and he found it hard to understand why the Pope would back an unprovoked military assault. But the Pope had his own ambitions; he wanted more control over the English church. Even Bishop Odo was cynical, though. ‘God guides us all, but it does no harm to back a winner, even if you’re the Pope.’ Anyway William’s embassy worked. Harold was actually excommunicated, and Odo was proudly able to display a papal banner for William’s forces to carry into battle.

All this may have been a pious justification for a vast act of robbery. But the strange thing about William was that he needed to believe it, utterly. For all his achievements, Orm saw, the Duke seemed to have a grievous fear of death and the punishment of God that could follow. He genuinely needed a holy pretext to justify the blood he spilled. In this, brother Odo was useful. The bishop provided the reassurances that helped the Bastard sleep at night.

With the Pope’s backing secured, William was able to present his expedition not just as a Norman adventure but a holy reconquest of a fallen Britain by a European coalition. William borrowed troops from the rulers of Flanders, Brittany and Aquitaine, and cast his net wide for mercenaries. Soon it seemed to Orm that every second son, bastard, murderer and rapist in Europe was drawn to William’s banner - all of them hard, experienced fighting men, and few of them with anything to lose.