They are deep and dark mysterious tunnels which were carved by the ancient people of Scotland whose purpose baffles scholars to this day.  

Often found beneath the remains of Iron Age dwellings and settlements, the hand-carved channels could have been used for storage, a ritual site, or even as a safe space to hide from marauding invaders. 

Probing the secrets of these ‘souterrains’ - named from a French phrase meaning underground passageway – has always been tedious and back-breaking work, forcing archaeologists to explore narrow confined crawlspaces often choked with centuries of rubble.  

But now technology is being used to speed up the process – and deliver maps of the age-old tunnels in detail never seen before.  

A team of archaeologists are using lasers to map out souterrains scattered about the Scottish Highlands at various sites that have previously been explored.  


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The method used involves a device called a Leica BLK360 laser scanner to study the site, which fires lasers at the walls 10,000 times a second. 

This creates a detailed 3D image of the site, from which measurements can be taken. 

These measurements then produce an interactive map of the souterrain, allowing archaeologists to study it without ever stepping foot in the dank tunnel. 

 

A team led by Graeme Cavers, of AOC Archaeology, is using the new technology to conduct research in a way impossible to do by hand. 

Manual measurements using a device called a theodolite—difficult to use in dark, cramped tunnels—have been replaced by these laser scanners, which have improved markedly in the past few decades.  

“They used to connect to an external laptop,” says Graeme cavers of AOC Archaology. “The data could only be recorded as fast as that connection. It was done over an Ethernet cable, so it was relatively fast.  

“But even then, the first laptops that I used with a scanner had 2 gigabytes of RAM. That was top of the range. And a laptop cost an awful lot of money in those days.” 


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Researchers turned their lasers on the Cracknie souterrain started February 2022. Cracknie, located in Borgies Forest, Scotland, is one of the best-preserved Iron Age souterrains in the country. 

The tunnel was built 2,000 years ago and is 13 meters long and one meter high. 

Some believe the tunnels were used for storage, but others claim they were used for unknown spiritual or religious practices, or even to imprison slaves and hostages. 

HeraldScotland:

A map of the souterrain

But now the full structure can be analysed above from the comfort of a computer screen, with a fraction of the effort required before.  

“To do the equivalent of what we did with a theodolite, you would be there a long time,” Cavers said. 

Forestry and Land Scotland, which enlisted the archaeologists for the project said: "Souterrains are still an enigma. 

“Perhaps they were for storage, such as grain in sealed pots or dairy products like cheese,” Matt Ritchie, resident archaeologist at Forestry and Land Scotland, told Wired magazine.  

“Perhaps they were for security, keeping valuables safe, or slaves or hostages secure. Or perhaps they were for ceremonial purposes, for household rituals, like a medieval shrine or private chapel.” 

"[Cracknie souterrain] is one of the most important scheduled monuments on Scotland's national forests and land.”