The walled fortified settlement, near the modern town of Provadia, dates to between 4,700 and 4,200 B.C., was home to around 350 people and was probably an important location for salt production, they said.
Water from a local spring was boiled and turned into salt brick for trade and to preserve meat, scientists said.
Salt was extremely valuable, which could be the reason for the defensive stone walls encircling the settlement, they said.
Archaeologists say they have also unearthed two-story houses, parts of a gate and a small burial ground, the BBC reported Wednesday.
The dating of the settlement puts it at least 1,500 years before the start of ancient Greek civilization, while similar salt production centers discovered in Bosnia and Romania help prove the existence of a series of civilizations in the Carpathian and Balkan mountains during the same period, researchers said.