Recent excavations at Provadia-Solnitsata, a 7,500 year old archeological site in southern Bulgaria that represents one of the earliest towns ever discovered in Europe, may help shed light on the links between mining, wealth, and trade in the ancient world.

Provadia-Solnitsata is an unusual site for the copper age. It was surrounded by stone walls ten feet tall and up to six feet thick, in a region where most other cities were protected by relatively flimsy palisade walls. Burials in a site nearby contain some of the earliest known hordes of gold in the region. The site is also one of the earliest to show systematized social inequality.

All of these things suggest that Provadia-Solnitsata was a place of great wealth, a place where the development of societal hierarchies and the increased efficiencies that go along with them may have occurred early on.

Although Provadia-Solnitsata is a copper age site, the thick walls of the site were not built to protect wealth built on copper. Instead, evidence points to the large scale mining and production of salt.

Salt was one of the most important mineral resources of the ancient world. For thousands of years, it was used as the major currency of the western hemisphere. Salt was essential for the preservation of food, it was easily transportable, and, most importantly, it was hard to come by.

At Provadia-Solnitsata, large kilns located within the settlement’s protective walls are thought to have been used to boil water from the brine springs. The residual salt was compressed into bricks, some of which were unearthed by archaeologists during the excavation.

Early kilns unearthed at the site, built around 5,500 BC, are estimated to have produced 25 kg of salt per load. By 4500 BC, the salt extraction industry seems to have expanded significantly – instead of 25 kg of salt, each kiln load was producing 4,000-5,000 kg of salt. To the archeologists excavating the site, this can only mean one thing – the development of a large scale trade network, with Provadia-Solnitsata at its center. If this is the case, the mining of salt may have been a critical part of the development of ancient societies in the region.

The site was ultimately abandoned around 4,200 bc when a changing climate made agriculture in the region unsustainable.

To learn more about the ruins at Provadia-Solnitsata and the associated salt production facilities, check out these articles:

National Geographic Article

Analysis by Vassil Nikolov, a Bulgarian archeologist involved with the project