They drove him right out of Athens, after someone found money stashed in the thatch of his house. Never had any explanation for what they were doing in the thatch of their house. And it was years before certain infamous cops planted dope in the Beatles' hotel rooms.
The Persians were so grateful to the Athenians, they made Themistocles adminstrator over one of their cities, in fact, I think they even rebuilt the city so that he'd have one to run.
That needs to be in the sequel to the sequel:
“300: Rise of City Hall - Boss Tweed-mistocles”!