Between the 8th and 6th centuries BCE, many Greek city-states (poleis) sent colonists to find new places to settle. Population growth in these small states and frequent wars with neighbors created a shortage of land to feed their people. The settlers looked for convenient harbors near fertile land and peaceful relations with the local populations. They especially valued proximity to ore deposits and trade opportunities with inland tribes. During this period, Greek colonies (apoikiai) were founded throughout the Mediterranean and along the Black Sea coast. Many of these cities still exist today.

The first Greek settlers on the Thracian shores of the Black Sea were Ionian Greeks from Miletus—a large and powerful city on the Aegean coast of present-day Turkey. In the second half of the 7th century BCE, they settled near the delta of the Istros (Danube River) in present-day Romania and established the ancient city of Histria. At the end of the 7th century BCE, Milesians, along with settlers from other Milesian colonies and their allies, founded Apollonia, now the city of Sozopol. The colonists named their new settlement to honor Miletus's principal patron god, Apollo the Healer.

In the 6th century BCE, Dorian Greeks from Megara—a city-state in mainland Greece—founded Mesambria (present-day Nesebar) and Callatis (present-day Mangalia in Romania). Other Greek apoikiai established during this period include Odessos (present-day Varna), Dionysopolis (present-day Balchik), Anchialos (present-day Pomorie), and Tomis (present-day Constanța in Romania).

The colonies maintained close ties with their mother cities (metropoleis), inheriting their gods, cults, customs, and systems of government. From the moment they arrived on the Thracian shores, the Greeks interacted and traded with neighboring Thracians. Over time, they ventured deep into Thrace's interior, bringing objects and fashions tied to the Greek way of life.

Between the 5th and 4th centuries BCE, Apollonia grew significantly thanks to its location and proximity to copper ore deposits. The city gained importance not only in the Western Black Sea region but also in Thrace's interior. As a symbol of their prosperity, the Apollonians erected a 13-meter-high bronze statue of Apollo. However, this statue was lost when the Roman general Marcus Lucullus conquered Apollonia in 72 BCE and took it to Rome. During the Hellenistic period (late 4th–2nd centuries BCE), Apollonia declined in power and population, while Odessos and Mesambria experienced a period of flourishing.