A 23-metre circular timber platform built more than 5,000 years ago has been uncovered beneath what was long taken for a stone-built artificial island in a Scottish loch, with radiocarbon dates from the Loch Bhorgastail crannog and other Outer Hebrides sites aligning to between 3500 and 3300 BC. That is according to a paper published this week in the journal Advances in Archaeological Practice by Dr Stephanie Blankshein and Professor Fraser Sturt of the University of Southampton, working with Dr Duncan Garrow at the University of Reading and Angela Gannon at Historic Environment Scotland under the AHRC-funded Islands of Stone project.
Wood Central understands the academic work was triggered by Lewis resident and local archaeologist Chris Murray, who in 2012 recovered extraordinarily well-preserved Early and Middle Neolithic pots from a loch bed, and who later worked with Mark Elliot of Museum nan Eilean to identify similar collections at five further crannog sites across the island.
The Bhorgastail platform was first established as a circular timber base 23 metres across, topped with brushwood, with later layers of brushwood and stone added during the Middle Bronze Age and further activity recorded during the Iron Age. Hundreds of pieces of Neolithic pottery were recovered from the loch bed surrounding the crannog, with a now-submerged stone causeway leading from the shore to the island.
Dr Blankshein said the excavation overturned earlier readings of the site, with the wood proving to be the load-bearing element rather than fill beneath a stone cairn. “The timber itself was the basis of the structure,” Dr Blankshein said.
Professor Sturt had described the crannogs in his 2019 commentary on the project’s first dating paper as a “monumental effort… to build mini-islands by piling up many tons of rocks on the loch bed,” with the 2021 excavation and the new photogrammetry method now confirming timber, not stone, as the load-bearing layer.
A diver from the University of Southampton works inside a measurement frame above the exposed timber substructure at Loch Bhorgastail, with brushwood and worked timbers visible beneath the stone cap that disguised the crannog as a stone island for 5,000 years until the team’s 2021 excavation. (Photo Credit: University of Southampton/PA)
The team developed a shallow-water photogrammetry technique to map the crannog above and below the waterline as a single continuous structure, using two waterproof low-light cameras mounted on a frame and manoeuvred by a diver to centimetre-level positioning, a technique the researchers say matches that of an aerial drone.
“This problem is a well-known frustration for archaeologists,” Professor Sturt said, citing fine sediments, choppy conditions, floating vegetation and reflected light as the conditions that hinder imaging at depths under one metre.
Crannogs sit at the boundary where shallow water of 3 to 4 metres meets depths of up to 20 metres, with over 550 examples recorded across Scotland and 170 known sites in the Outer Hebrides alone, although only 10 per cent have been radiocarbon dated and just 20 per cent dated at all.
It comes as Wood Central reported on a 1,200-year-old Carolingian-era ship timber unearthed during sewer works at the former Frankish trading port of Dorestad in the Netherlands, with both finds anchored in the same point: structural timber surviving longer in the ground than the civilisations that built it.
Substantial quantities of Neolithic ceramic vessels were recovered, largely intact, from the lochs around the crannog and other Outer Hebrides sites, suggesting systematic, possibly ritualised, deposition from the islets rather than incidental loss. Of an estimated 170 crannogs across the Outer Hebrides, only one in five has been dated by any method, with the new shallow-water imaging technique now positioned to extend the AHRC-funded Islands of Stone survey across the remaining 136 sites.
