They say 'slave' sorts not with 'Athenian.'
It;s curious the use of language here. While this is saying that the Athenians are slave to none, that they do not have one ruler above them as they are a democratic power, the use of "slave" not sorting with Athenian is an interesting choice of words because they do house slaves. So while what the author is saying is true, the use of the word slave here is an interesting choice as the word slave does correlate to Athens, but not in the same way. It's almost to indicate, as the original author was Athenian, that they are superior to Persia because they bow to no one man, no king rules Athens. They are not subjugated to another people, like most of Persia's territory, which are satraps and subjugates of Persia, and not all technically Persians.
Zach Long CC BY-NC-ND