Sofia - Archaeologists in eastern Bulgaria say they have unearthed the oldest prehistoric town ever found in Europe, along with an ancient salt production site that gives a strong clue about why massive riches were discovered in the region.Excavations at the site near the modern-day town of Provadia have so far uncovered the remains of a settlement of two-storey houses, a series of pits used for rituals as well as parts of a gate, bastion structures and three later fortification walls - all carbon dated between the middle and late Chalcolithic age from 4 700 to 4 200 BCE (Before Common Era)."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," said Vasil Nikolov, a researcher with Bulgaria's National Institute of Archaeology, after announcing the findings earlier this month.Nikolov and his team have worked since 2005 to excavate the Provadia-Solnitsata settlement, located near the Black Sea resort of Varna.A small necropolis, or burial ground, was also found this year, but has yet to be studied more extensively and could keep archaeologists busy for generations.Production centreArchaeologist Krum Bachvarov from the National Institute of Archaeology qualified this latest find as "extremely interesting" due to the peculiar burial positions and objects found in the graves, which differed from other Neolithic graves found in Bulgaria."The huge walls around the settlement, which were built very tall and with stone blocks... are also something unseen in excavations of prehistoric sites in southeast Europe so far," Bachvarov added.Well fortified, a religious centre and most importantly, a major production centre for a specialised commodity that was traded far and wide, the settlement of about 350 people met all the conditions to be considered the oldest known "prehistoric town" in Europe, the team says."At a time when people did not know the wheel and cart these people hauled huge rocks and built massive walls. Why? What did they hide behind them?" Nikolov asked.The answer: "Salt."The area is home to huge rock-salt deposits, some of the largest in southeast Europe and the only ones to be exploited as early as the sixth millennium BCE, Nikolov said.This is what made Provadia-Solnitsata what it was.Different significanceNowadays, salt is still mined there but 7 500 years ago it had a completely different significance."Salt was an extremely valued commodity in ancient times, as it was both necessary for people's lives and was used as a method of trade and currency starting from the sixth millennium BC up to 600 BC," the researcher explained.Salt extraction at the site first began in about 5 500 BCE when people started boiling brine from the nearby salty springs in dome kilns found inside the settlement, Nikolov said, citing carbon dating results from a British laboratory in Glasgow."This is the first time in southeast Europe and western Anatolia that archaeologists have come upon traces of salt production at such an early age, the end of the sixth millennium BC, and managed to prove it with both archaeologic and scientific data," Bachvarov confirmed.Salt production was moved outside the settlement toward the end of the sixth millennium and productivity gradually increased. After being boiled, the salt was baked to make small bricks.Nikolov said production increased steadily from 5 500 BCE, when one load from the kilns in Provadia-Solnitsata yielded about 25kg of dry salt. By 4 700 - 4 500 BCE, that amount had increased to 4 000kg to 5 000kg of salt."At a time when salt was as precious as gold you can imagine what this meant," he said.Economic powerThe salt trade gave the local population huge economic power, which could explain the gold riches found in graves at the Varna Necropolis and dating back to around 4 300 BCE, Nikolov suggested.The 3 000 jewellery pieces and ritual objects have been internationally recognised as the oldest gold treasure in the world, raising questions as to how a culture of farmers and stock-breeders from a region otherwise poor in natural resources could acquire such wealth.The excavations have however suffered from a chronic lack of state funding, which Nikolov replaced with private donations.A British anthropologist, a Japanese ceramics expert and a team of radiocarbon specialists from Germany have worked on the site for free this season.