Trou du Calel

Trou du Calel is a large cave system on the northern flank of the Montagne Noire, in the commune of Sorèze in the Tarn department of southern France. Beneath the limestone causse plateau lies a rare combination: a natural cave that was also worked as a medieval iron mine, making Calel one of the most unusual underground sites in the Occitanie region.

How big is the underground network?

Cavers have so far surveyed more than 7 kilometres of galleries and chambers, with a vertical range of over 130 metres, making Calel the longest natural cavity recorded in the Tarn department. Inside, the character shifts from narrow, winding passages to broad chambers, some of them carrying an underground stream. Water carved these passages out of the plateau's limestone over an immense span of time, long before anyone set foot underground to mine it.

Why was it mined?

The rock here contains deposits of iron oxides, including goethite, and from roughly the 11th to the 12th century, Calel was worked as an iron mine. Radiocarbon dates taken from material recovered underground point to activity spanning the 10th to 13th centuries, with a clear peak between about 1050 and 1150. Excavators also found the remains of a direct-reduction furnace in one of the chambers, showing that ore was smelted right where it was extracted rather than hauled to the surface first.

What did the miners leave behind?

This is where Calel becomes genuinely rare. Charcoal drawings survive on the cave walls, including a human figure - a miner shown holding a pick, with a basket carried on his back. Medieval mining imagery of this kind is exceptionally uncommon, and together with the nearby smelting furnaces it makes Calel a unique record of underground labour from a thousand years ago. Archaeologists have also recovered fragments of pottery lamps that once burned oil, soot marks left by torches, remnants of wooden scaffolding, and stairs cut into stone and clay. Footprints preserved in the damp ground include some belonging to children roughly 6 to 8 years old, evidence that young children took part in the mining work. At the bottom of one shaft, excavators found a human skeleton, most likely someone who died in a fall.

Can you visit the cave?

The Calel cave has been protected as a Monument Historique since 1977, with the protected zone extended in 1991 and 1995 to cover additional plots and their subsoil. Because the archaeological remains are fragile and the underground terrain can be hazardous, the cave itself is not open for casual visits - entry is only possible with authorisation as part of organised access. Above ground, however, a well-known walking trail passes near the cave entrances and continues to the nearby Oppidum de Berniquaut hillfort, forming a loop of around 6.8 km that takes about 2 to 2.5 hours and crosses land also valued for its causse landscape and ecology.

Frequently asked questions

Where is Trou du Calel located? In the commune of Sorèze, on the northern slope of the Montagne Noire, in the Tarn department.

How extensive is the Calel cave system? Over 7 km of galleries have been mapped, with a vertical range of more than 130 metres - the longest known natural cave in Tarn.

When was iron mined here? Mainly during the 11th and 12th centuries, with radiocarbon dating showing activity from the 10th to the 13th century and a peak around 1050-1150.

Can you go inside the cave on your own? No - the cave is protected as a Monument Historique and entry requires authorisation. A surface trail does pass by the entrances on its way toward the Oppidum de Berniquaut.