Moderatio is the word from which we get our English word, moderation. It means governance or control, guidance, regulation. For Aristotle, the concept of moderation is central to the entire notion of “virtue”, since he said that virtue itself is having neither an excess nor a deficit of a trait. Ancient Romans adored Greek philosophy, and moderation was a key Greek virtue. Entire branches of philosophical thought, such as Epicureanism, were based on the ideal of moderation.
As modern people, we tend to think of moderation in terms of temperance. Like Aristotle, we define being moderate by being not too extreme and by not under or overdoing things. To be moderate is to be “in the middle” and to strive for balance in our actions. Epicurus is one of the progenitors of the Wiccan idea of “do no harm”, and many people who consider themselves moderates embrace a similar notion. Moderates view extreme behavior as being harmful to people and society, and tend towards a “live and let live” ethic. Unfortunately, I think this can be a too passive form of moderation.
I think the Romans would have viewed moderatio primarily through the lens of self-control. To practice moderatio would be to actively practice self-regulation. It’s one thing to be moderate when it’s convenient or expedient to do so, and another to practice it actively. If the point of moderation is to avoid harm, then simply sinking into passive inaction and calling it moderate behavior won’t suffice. True moderation requires active self-governance, and taking action when needed, either by restraining one’s actions or by doing something to correct the unbalanced situation.