For the sake of this question I'm defining "classical" as "Pre-Renaissance." I am looking for quotes or sources from authors recognized as political theorists or philosophers, but if you've got interesting bits from correspondence between rulers/leaders I'm here for it.
One example of this is Plato said (addressing Glaucon), from The Republic:
And therefore every care must be taken that our auxiliaries, being stronger than our citizens, may not grow to be too much for them and become savage tyrants instead of friends and allies?
Is there anything else about this topic from the “classical” time period?