Archaeologists in Bulgaria say they have discovered the oldest prehistoric town found to date in Europe.

Remains of a walled fortified settlement, including two-storey houses, a series of pits used for rituals and bastion structures, were unearthed during excavations at a site near the modern-day town of Provadia. The town has been carbon-dated between the middle and late Chalcolithic age -- from 4,700 to 4,200 BC -- and is believed to have been home to an estimated 350 people.

The period dates back to about 1,500 years before the start of the ancient Greek civilization.

The residents are believed to have produced salt by boiling water from a local spring and traded it. They used it for preserving meat.

A small necropolis or a burial ground was also discovered at the site earlier this year. The cemetery of several thousand square meters is at about 250 meters to the southwest of the settlement mound.

"We are not talking about a town like the Greek city-states, ancient Rome or medieval settlements, but about what archaeologists agree constituted a town in the fifth millennium BC," Vassil Nikolov, a researcher with Bulgaria's National Institute of Archeology, told AFP.

Archeologist Krum Bachvarov from the National Institute of Archeology told AFP that the huge walls around the settlement were something unseen in excavations of prehistoric sites in southeast Europe thus far.

Nikolov said the people, who didn’t conceivably have any valuables to hide, built high walls to secure salt, which was considered a valuable commodity back then.

“A premise for the prosperity of the society in the later prehistory (6th and 5th millennia BC) in the region of Provadia-Solnitsata was the salt that in the early agricultural period became the only strategic resource,” Nikolov says in a paper titled “Salt, early complex society, urbanization: Provadia-Solnitsata.”

He says according to the criteria accepted for the period, the prehistoric settlement of Provadia could be defined as a prehistoric city since they specialized in salt production and had successful long distance trade.