To the 5th-century historian Thucydides, the Epirotes were "barbarians." The only Epirotes regarded as Greek were the Aeacidae, who were members of the Molossian royal house and claimed descent from Achilles.
From about 370 BC on, the Aeacidae were able to expand the Molossian state by incorporating tribes from the rival groups in Epirus.
The Aeacidae's efforts gained impetus from the marriage of Philip II of Macedon to their princess, Olympias.