Final answer:
The Norman Conquest in 1066 brought the Old English Period to an end.
Step-by-step explanation:
The event that brought the Old English Period to an end was the Norman Conquest in 1066. In this event, William the Conqueror, a Viking-descended king from Normandy in northern France, invaded and defeated the Anglo-Saxon king, establishing Norman rule in England. This marked a significant change in the political and cultural landscape of England and had a lasting impact on the English language.