The walled fortified settlement, near the modern town of Provadia, is thought to have been an important centre for salt production.
Its discovery in north-east Bulgaria may explain the huge gold hoard found nearby 40 years ago.
Archaeologists believe that the town was home to some 350 people and dates back to between 4700 and 4200 BC.
That is about 1,500 years before the start of ancient Greek civilisation.
The residents boiled water from a local spring and used it to create salt bricks, which were traded and used to preserve meat.
Salt was a hugely valuable commodity at the time, which experts say could help to explain the huge defensive stone walls which ringed the town.
'Extremely interesting' Excavations at the site, beginning in 2005, have also uncovered the remains of two-storey houses, a series of pits used for rituals, as well as parts of a gate and bastion structures.
A small necropolis, or burial ground, was discovered at the site earlier this year and is still being studied by archaeologists ( via bbc.co.uk ).