Final answer:
Castles were built to be safe and secure fortifications during the medieval period.
Step-by-step explanation:
The correct answer is D. They were built to be safe.
Castles were fortifications built during the medieval period to provide protection and defense. They were designed with strong defensive features such as thick walls, towers, and sometimes moats, making them difficult to attack.
Examples of famous castles include the Tower of London in England and the Château de Versailles in France.
Learn more about Castles and their purpose