Conny Waters – Ancientpages.com – Why was an artificial island, predating even Stonehenge, constructed in Loch Bhorgastail on the Isle of Lewis? What purpose did it serve for the people who invested so much effort to build it, and what does it reveal about their beliefs, needs, and relationship with the landscape around them?
Archaeologists have excavated and documented a substantial timber platform concealed beneath what currently appears to be a stone-built island in a Scottish loch.
Researchers from the University of Southampton employed a technique known as stereophotogrammetry to record the human-made island both above and below the waterline as a single, continuous structure, thereby achieving a perspective that would not have been possible through land-based or underwater survey methods alone.
Aerial view of the Loch Bhorgastail crannog. Credit: Blankshein S. et al. 2026
In collaboration with the University of Reading, the team investigated the ‘crannog’ in Loch Bhorgastail on the Isle of Lewis and identified a structure constructed more than 5,000 years ago. Their fieldwork revealed a layered arrangement of timber and brushwood beneath the island’s stone surface, as well as hundreds of Neolithic pottery fragments submerged in the surrounding waters.
“Crannogs are small artificial islands that are typically thousands of years old. Hundreds exist in the lochs of Scotland and many remain unexplored or undiscovered.
While crannogs were long thought to have been built, used and re-used, mainly between the Iron Age and the post-medieval period, we now know that some were first constructed much earlier during the Neolithic between 3800 and 3300 BC,” University of Southampton archaeologist Dr Stephanie Blankshein explains.
Why Were These Artificial Islands Built?
Over several years of dedicated fieldwork, archaeologists have carefully explored the Loch Bhorgastail crannog using traditional excavation, coring, advanced surveying, and radiocarbon dating. Their patient, meticulous efforts have illuminated the remarkable stages of the site’s development.
The crannog at Loch Bhorgastail. Credit: University of Southampton
First established over five thousand years ago—older than iconic monuments like Stonehenge—the crannog began as a circular wooden platform about 23 meters across, covered with brushwood. Around two thousand years later, in the Middle Bronze Age, another layer of brushwood and stone was thoughtfully added. A further phase of activity took place roughly a thousand years after that, during the Iron Age. Today, a stone causeway, now submerged, still connects the loch shore to the island, a quiet testament to the ingenuity of its builders.
Over time, archaeologists have also recovered hundreds of pieces of Neolithic pottery, such as fragments of jars and bowls, from the surrounding waters. These finds strongly suggest that the site was first established by Neolithic communities, long before the Bronze Age, highlighting the deep and enduring human story preserved at Loch Bhorgastail.
“While we still don’t know exactly why these islands were built, the resources and labour required to construct them suggests, not only complex communities capable of such feats, but also the great significance of these sites. Large quantities of pottery, often still containing food residue, and worked stone found on and around the islands, suggest their use for communal activities such as cooking or feasting,” says Dr. Blankshein.
Seeing Clearly In Shallow Water
During fieldwork in 2021, archaeologists designed and implemented an innovative technique for using stereophotogrammetry in shallow water. By applying this image-capturing process to examine the loch bed surrounding the crannog, they opened up valuable new possibilities for underwater archaeological research. Their carefully developed method is now shared in a newly published article in the journal Advances in Archaeological Practice, offering an important contribution to the field.
Excavating underwater at the loch. Credit: University of Southampton
Photogrammetry is a well-established, highly regarded technique for creating 3D computer imagery from multiple 2D photographs. By capturing images of a subject from many different angles and then ‘stitching’ them together with specialist software, researchers can produce high-resolution digital models that greatly enhance our understanding and documentation of archaeological sites.
Successfully conducting photogrammetry in shallow water is, however, fraught with obstacles, as Principal Investigator and Director of the Southampton Marine and Maritime Institute, Professor Fraser Sturt, explains: “Fine sediments, choppy conditions, floating vegetation, and distorted or reflected light all hinder shallow water imaging. Photogrammetry is very effective in deep water but runs into problems at depths of less than a meter. This problem is a well- known frustration for archaeologists.”
The crannog’s timber platform below the waterline. Credit: University of Southampton
To address this challenge, the researchers employed two compact, waterproof cameras featuring low-light capabilities and a wide field of view. Mounted at a fixed distance apart on a frame, this stereo configuration enabled precise image overlap, thereby compensating for any missing or disrupted data.
Fragments of a Neolithic pot found near the crannog. Credit: University of Southampton
The cameras were guided through the water by a diver, with their position controlled to centimeter-level accuracy, comparable to that achieved by an aerial drone.
“By combining stereophotogrammetry, drone technology and some innovative post-processing of the data, we have managed to set out an accessible approach that is portable and cost-effective,” says Dr. Blankshein, lead author on the paper.
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This innovative surveying work represents the first publication from the University of Southampton’s Coastal & Inland Waters Heritage Science Facility. This work has provided extra clues to the mysterious past of the crannog structures, and the team hopes the method can now help further investigations of other, similar sites.
The study was published in Advances in Archaeological Practice
Written by Conny Waters – AncientPages.com Staff Writer