Brewer's Dictionary of Phrase and Fable/Abderitan
Abderi′tan. A native of Abdēra, a maritime city of Thrace. The Abderītans were proverbial for stupidity, hence the phrase, "You have no more mind than an Abderite." Yet the city gave birth to some of the wisest men of Greece: as Democrītos (the laughing philosopher), Protagōras (the great sophist), Anaxarchos (the philosopher and friend of Alexander), Hecatæos (the historian), etc.