Abdera, in ancient Greece, town on the coast of Thrace near the mouth of the Néstos River. The people of Teos, evacuating Ionia when it was overrun by the Persians under Cyrus (c. 540 bc), succeeded in establishing a colony there that developed a brisk trade with the Thracian interior. Abdera was a prosperous member of the Delian League in the 5th century but was crippled early in the 4th century bc by Thracian incursions and declined sharply in importance. The philosophers Protagoras and Democritus were citizens of Abdera. The site is occupied by the modern town of Ávdhira, Greece.