What happened
William, duke of Normandy, defeated the army of King Harold II near Hastings after crossing the Channel to press his claim to the English throne. Harold was killed in the battle, and the victory broke the military resistance of the existing English regime.
Why it matters
This is the decisive military event of the Norman Conquest. It opened the way for William's accession and for the transformation of English kingship, aristocratic landholding, and England's relationship to the continent.
Notes
Use this as the main event anchor for the conquest itself, even though the wider process of consolidation continued after 1066.