Archaeologists exploring the prehistoric salt mine at Hallstatt in Austria have discovered an extensive network of previously unknown Iron Age mining chambers stretching for at least 300 metres beneath the mountain.
The discovery was made during exploratory drilling carried out by archaeologists from the Natural History Museum Vienna (NHM), who are investigating areas of the ancient mine that have remained beyond the reach of modern researchers.
Rather than revealing a single enormous underground cavity, as initially suspected, drilling showed that prehistoric miners had created a series of parallel chambers positioned at different levels inside the mountain.
Daniel Brandner, head of underground excavations at the NHM’s Prehistoric Department, said archaeologists had never previously encountered such an arrangement at Hallstatt.
The newly identified workings provide an unusual glimpse into Iron Age mining from around the sixth century BC, when Hallstatt was already one of Europe’s most important prehistoric centres of salt production.
Thousands of years of salt mining
People were exploiting the salt deposits in the high valley above Hallstatt in Upper Austria thousands of years before the Iron Age.
Evidence indicates that humans were present there around 7,300 years ago, with Neolithic antler picks and stone tools discovered within the mountain providing some of the earliest evidence for salt extraction.
Mining subsequently expanded dramatically. By around 1200 BC, production had reached what researchers describe as an almost industrial scale, with an estimated 1.5 tonnes of salt being extracted each day.
The operation was repeatedly disrupted by major landslides that sent material from the surface into underground workings and filled previously excavated spaces.
Yet the community repeatedly returned. According to Brandner, archaeological evidence suggests salt production could resume only a few years after such disasters, demonstrating the resilience of the prehistoric population and the importance of the resource to the local economy.
Mining continued into the Iron Age, including during the sixth century BC.
One of Hallstatt’s most remarkable discoveries is associated with this period. In 1734, miners encountered the exceptionally preserved remains of a man inside the salt mine. The individual, subsequently known as the “Man in the Salt”, is thought to have been an ancient miner killed during a catastrophic event underground.
His true antiquity was not understood when the body was discovered, however, and his remains were later buried in Hallstatt’s cemetery.
Drilling reveals previously unknown chambers
Much of what archaeologists know about prehistoric activity beneath Hallstatt has historically depended on chance.
Ancient workings have generally been discovered only where later mining tunnels happened to intersect them, leaving potentially extensive sections of the prehistoric mine unexplored.
Researchers began addressing this problem in 2022 by using a core drilling system supplied by Salinen Austria AG. Normally employed for geological investigation, the equipment can drill hundreds of metres through the mountain and allows archaeologists to search for ancient workings without first excavating large new tunnels.
The programme has now revealed an unexpectedly extensive Iron Age mining landscape.
Researchers have traced the newly identified workings for approximately 300 metres. Individual chambers are estimated to have reached around 25 metres in width and roughly 20 metres in height.
Their parallel arrangement appears to reflect a sophisticated understanding of the mountain’s geology. Rather than excavating indiscriminately, Iron Age miners followed the natural deposits of rock salt and adapted the shape of their workings accordingly.
Nine metres of prehistoric mining debris
Perhaps even more significant than the scale of the chambers is what survives on their floors.
Researchers have identified deposits of mining debris measuring as much as nine metres thick in places.
These layers contain material discarded or lost by generations of miners, including burnt pine splinters used for lighting, damaged tools, fragments of clothing and other organic objects.
Human excrement has also survived. Salt creates exceptional preservation conditions for organic materials that would normally disappear from archaeological sites, allowing researchers to recover evidence rarely available elsewhere.
The upper portions of the chambers, which would once have been open working spaces, are now filled with material that entered from the surface, probably during a major landslide.
Initial excavation of the deposits is beginning to reveal details of an Iron Age phase of mining that archaeologists have previously understood only imperfectly.
Researchers can investigate not simply where miners worked, but how they extracted salt, what equipment they carried, what they wore and even what they ate.
Clothing, tools and ancient DNA
Among the finds are textiles and fragments of garments preserved by the salty environment, together with wooden vessels that still contain traces of food.
Mining tools are also providing evidence for technological change.
Earlier equipment from Hallstatt was often highly standardised, with tools specifically designed for particular mining techniques. Finds from the newly investigated Iron Age workings suggest this system changed considerably during the period.
Archaeologists have identified different forms of tool hafts, potentially reflecting new approaches to extracting salt.
Intriguingly, the material discovered at Hallstatt also shows striking similarities to finds from the prehistoric salt mines at Dürrnberg near Hallein in Salzburg, where large-scale salt extraction began around the sixth century BC.
The parallels could help researchers understand whether mining communities in the two regions shared technology, practices or wider cultural traditions.
The preservation of human waste and food remains could provide another major source of evidence.
Genetic material belonging to individual miners can potentially survive within these deposits, while DNA belonging to plants and animals they consumed may also remain preserved in the sediment.
Such evidence could allow scientists to reconstruct aspects of the miners’ diet, health and daily lives with a degree of detail rarely possible for Iron Age communities.
Old excavation sites reopened for modern research
Alongside exploration of the newly discovered chambers, archaeologists are working with the modern saltworks and mine operators on a wider project to reopen historic archaeological areas within the mountain.
Some have been inaccessible to researchers for decades.
Reaching them requires the restoration and reinforcement of tunnels that can themselves be between 200 and 300 years old. Infrastructure is also being installed to make the underground areas safe and accessible for future scientific work.
The project, supported by Austria’s federal government and the state of Upper Austria, will allow archaeologists to return to sites investigated by previous generations and examine them using modern techniques unavailable when the original excavations took place.
That could include genetic analysis, microscopic examination, environmental reconstruction and other methods capable of extracting information from material that earlier researchers could not study.
For archaeologists, Hallstatt represents an exceptional archive of prehistoric European life. Its salt deposits have preserved materials that would normally decay, while thousands of years of mining activity have left an extensive record hidden inside the mountain.
The newly discovered Iron Age chambers suggest that significant parts of that record remain unexplored.
Researchers will present their latest findings during the “Archaeology on the Mountain” event at Hallstatt on 12 and 13 September. This year’s programme will focus on the development of salt transportation from prehistoric times to the modern era, alongside the continuing archaeological investigation of one of Europe’s most extraordinary ancient mining landscapes.
Header Image Credit : D. Brandner/NHM Wien
Sources : NHM
