Archaeologists have uncovered the secrets of an artificial island in Loch Bhorgastail on the Isle of Lewis, revealing a large timber platform hidden beneath its stone surface. The crannog, which dates back to around 3500–3300 BC, is older than Stonehenge and was constructed using a substantial wooden structure as its foundation.
Researchers from the University of Southampton, in collaboration with the University of Reading, used stereophotogrammetry to create 3D imagery of the island, showing it as a single continuous structure above and below the waterline. Excavations in 2021 uncovered a layered wood and brushwood construction under the stone, along with hundreds of Neolithic pottery pieces submerged in the surrounding water.
Dr Stephanie Blankshein, an archaeologist at the University of Southampton, said: “When we actually started excavating is when we realised that it was actually this coherent, quite large timber structure that was under what you would see as the stone island today. Before that, we didn’t know. We just knew that there were pieces of wood sticking out and that there must have been some sort of structure there.”
The crannog was first established more than 5,000 years ago as a circular wooden platform, around 23 metres across, topped with brushwood. Around 2,000 years later, in the Middle Bronze Age, another layer of brushwood and stone was added, with further activity during the Iron Age. A stone causeway, now underwater, connects the loch shore to the island.
Professor Fraser Sturt, principal investigator and director of the Southampton Marine and Maritime Institute, explained the challenges of shallow-water photogrammetry: “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 metre.” The team developed a new technique using two small waterproof cameras on a frame, manoeuvred by a diver with centimetre accuracy, to capture overlapping imagery.
Dr Blankshein added: “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.” The findings provide new insights into Neolithic and Bronze Age communities in the Outer Hebrides.
