Later, people were frightened of the Romans, and the cities were good places (4) _________.

Knowledge: The form of the verb

When we want to express purposeful action, we use the verb form to + V infinitive

=> Later, people were frightened of the Romans, and the cities were good places to hide.

After that, people were afraid of the Romans, and cities were good places to hide.

The answer to choose is: EASY