It was a fatal mistake, as William rallied his men and routed the unprotected attackers.
The Saxon lines quickly closed, but they had not learned their lesson, and they repeated the same folly of chasing an apparently fleeing enemy twice more as the day wore on.
By late afternoon the Saxon lines were wavering under continued Norman attacks.
It is then that the most famous arrow in English history was released by an anonymous Norman archer.
The arrow took King Harold in the eye, and a final Norman onslaught killed him where he stood.
The rest of the leaderless Saxons ceded Senlac ridge yard by grudging yard, but eventually they had no choice but to turn and flee the field. The day belonged to Duke William, soon to be dubbed, "the Conqueror".
The body of King Harold was eventually buried in Waltham Abbey.
Although there were sporadic outbreaks of Saxon resistance to Norman rule after the Battle of Hastings - notably in East Anglia under Hereward the Wake, and in the north of England - from this point on England was effectively ruled by the Normans.