Final answer:
The fall of the Roman Empire is usually considered the beginning of the Middle Ages in Europe.
Step-by-step explanation:
The event that is usually considered the beginning of the Middle Ages in Europe is a) The fall of the Roman Empire. The Middle Ages or Medieval period started with the collapse of the Western Roman Empire in 476 CE. It was a time of political and military discord, with Europe experiencing internal conflicts and invasions from outsiders. During the Middle Ages, feudalism emerged, and people lived in walled cities seeking protection from marauding pillagers.