Sections of Thrace, particularly in the south, had started to become hellenized before the Peloponnesian War as a significant amount of Athenian and Ionian colonies were set up in Thrace before the war and Spartan and other Doric colonists followed suit after the war.

In 168 BCE, after the Third Macedonian war and the subjugation of Macedonia to the Romans, Thrace also lost its independence and became tributary to Rome, while towards the end of the first century BC it was a client kingdom of the Romans, who appointed their kings until CE 46, when the Romans finally turned Thrace into a Roman province (Romana provincia Thracia).During the Roman domination, within the geographical borders of ancient Thrace, there are two separate Roman provinces, namely Thrace ("provincia Thracia") and Lower Moesia ("Moesia inferior").

Later, in the times of Diocletian, the two provinces are joined and form the so-called "Dioecesis Thracia".