Bennett's New Latin Grammar (this link will take you to appropriate section) offers several helpful rules of thumb for the agreement of an adjective with multiple nouns.
Although I recommend reading the above entry, which is fairly short, the basic principles are:
- Attributive adjectives agree with the nearest noun in both gender and number, e.g. "Filius meus et soror" vs. "Filius et soror mea"
Predicative adjectives are made plural and:
- agree with the nouns if they are the same gender, e.g. "Filia et mater mea sunt pulchrae"
- are masculine if the nouns are persons, e.g. "Soror et frater inepti sunt."
- are neuter if the nouns are things, e.g. "urbes et moenia foeda sunt"
If the nouns are mixed, things get more arbitrary and there do not seem to be hard and fast rules, beyond what a Latin ear tells you is right.
In the case you mention, the above rules would indicate the neuter plural (visitata). Here too, though, I do not think there is a wrong or right answer, and my own inexperienced ear would feel more comfortable with the feminine plural because of the juxtaposition with Roma.