Uncovering the Secrets of an Ancient Scottish Crannog

Archaeologists have recently uncovered fascinating insights into an ancient artificial island located in Loch Bhorgastail on the Isle of Lewis, revealing a structure that predates Stonehenge. This discovery has shed light on the construction techniques and historical significance of this mysterious site.

The island appears to be made of stone, but research conducted by the University of Southampton has revealed that it was originally built using timber as its foundation. While some wooden remnants were known to exist beneath the surface, it wasn’t until excavation and analysis began that the full extent of the timber structure was understood.

During fieldwork at the crannog, archaeologists discovered a layered construction of wood and brushwood beneath the stone. They also found hundreds of pieces of Neolithic pottery submerged in the surrounding water.

Dr Stephanie Blankshein, an archaeologist from the University of Southampton, explained: “When we actually started excavating, we realized that it was a coherent, quite large timber structure under what you would see as the stone island today. That was a big surprise, and it happened in 2021 when we started digging down. Before that, we didn’t know. We just knew there were pieces of wood sticking out and that there must have been some sort of structure there.”

Working with experts from the University of Reading, the team used a technique called stereophotogrammetry. This involves creating 3D computer imagery using multiple 2D photos, allowing them to visualize the island both above and below the waterline as a single continuous structure.

Dr Blankshein added: “Through excavating and through the photogrammetry work we did, we were able to build a picture of this coherent timber structure. It wasn’t just bits of wood supporting a stone mound with a timber platform underneath. The timber itself was the basis of the structure.”

Radiocarbon dating has shown that the site dates back to around 3500 to 3300 BC, suggesting that similar activities were taking place across other nearby sites and even on other islands in the Outer Hebrides.

Crannogs are small artificial islands typically thousands of years old, with hundreds of them found in Scotland’s lochs. Dr Blankshein noted: “While we still don’t know exactly why these islands were built, the resources and labour required to construct them suggest not only complex communities capable of such feats, but also the great significance of these sites.”

The archaeologists have studied the development of the crannog over several years of fieldwork. Using traditional excavation techniques, radiocarbon dating, surveying, and coring, they discovered that the site was first established more than 5,000 years ago. Initially, it was a circular wooden platform around 23 metres across, topped with brushwood.

Around 2,000 years later, during the Middle Bronze Age, another layer of brushwood and stone was added. More activity occurred approximately 1,000 years after that during the Iron Age. A stone causeway, now underwater, once connected the island to the shore.

The site was first discovered in 2009. The researchers have since provided new perspectives using photogrammetry. This technique involves taking photographs from multiple angles and stitching them together to create a high-resolution digital model.

Carrying out photogrammetry in shallow water like that around the crannog presents challenges. Fine sediments, choppy conditions, floating vegetation, and distorted or reflected light all hinder imaging. While photogrammetry is effective in deep water, it struggles at depths of less than a metre.

To overcome these difficulties, the team developed a new technique during their fieldwork in 2021. They used two small waterproof cameras with low-light performance and a wide-field of view. These were locked at a set distance apart on a frame, ensuring precise overlapping of imagery to compensate for missing or disrupted data.

The cameras were maneuvered through the water by a diver, with positioning controlled to centimetre accuracy—matching that achieved by an aerial drone. Their technique is detailed in a newly published article in the journal Advances in Archaeological Practice.