Aerial photograph and map of Grassholm showing all identified features from previous archaeological surveys.

 Aerial photograph of Grassholm Island

At first glance Grassholm can be perceived as an inhospitable little island 25km off the west coast of Pembrokeshire. Look closer however and the island begins to show signs of a special place teaming with history and activity. Today, between March and October, the island is home to up to 39,000 Northern Gannets who travel to the island from as far as Africa and the Mediterranean countries to breed and nest. Amongst the thousands of gannet nests and deserted puffin burrows however are the remains of mysterious stone structures inter-linked by old stone field boundaries. Past humans unquestionably exploited the island before its colonisation by puffins and gannets, but their motives have always been unclear. Recent research by CHERISH has illuminated some of the island’s mystery through exploring and recording its rapidly eroding archaeology.

Previous archaeological investigations of the island have been pretty inconclusive. The first documented archaeological discoveries came in the early 20th century when a small collection of pottery, flint flakes and burnt stones were documented as being extracted from the site of ‘ancient dwellings’ across the island. Interestingly, the pottery was identified as being of likely Iron Age and Roman date which would suggest that humans were on the island as early as 2,000-3,000 years ago. Throughout the rest of the 20th century further surveys were carried out by Douglas Hague of the Royal Commission who recorded evidence of settlement and enclosures. Later field visits and aerial surveys carried out by archaeologists began to unveil more and more settlement structures including several possible roundhouses towards the centre of the island. These surveys also began to highlight for the first time the negative impacts the gannets were having upon the archaeology. Not only were they slowly eroding all the vegetation on the island with their nest building and extremely acidic guano, but they were also eroding the valuable archaeological remains.

map of Grassholm showing all identified features from previous archaeological surveys.

Map of Grassholm showing all identified features from previous archaeological surveys.

In response to the erosional threats posed by the wildlife and environmental pressures CHERISH headed out to record and research the threatened archaeology before more was lost. 2017 saw the first ever 3D LiDAR (airborne laser scanning) survey flown for the island which allowed for the precise identification and mapping of all upstanding archaeological features that had survived the gannets. From this work a few areas of interest were identified which were investigated during a 2019 visit by CHERISH. The main priority for the team was to undertake a rapid two-day evaluation excavation of a single stone-built structure towards the centre of the island that had become exposed due to the erosion of the previously overlying vegetation. A small segment of the one of the structure’s walls was excavated to characterise the way in which it was constructed and to recover any possible artefactual evidence. The results were a bit of a mixed bag with the team experiencing both joy (at the archaeology) and disgust (at the sheer amount of gannet guano).

Excavation within the building approaching the water table. The neat inner face of the west wall can be seen to the right of Louise

Excavation within the building approaching the water table. The neat inner face of the west wall can be seen to the right of Louise

Whilst it was known that the island is home to one of the densest gannet colonies in the world (accounting for around 10% of their total world population) their impact upon the island’s soils was not expected. The team essentially had to excavate through deposits almost entirely composed of gannet faeces and feathers. This was made worse by the fact that the water table at the trench’s location was only centimetres beneath the ground surface which turned the ‘soil’ into an unpleasant sludge. Hitting the water table may have however come as a relief to the team who had an excuse to stop excavating! Whilst the digging was pretty unpleasant the wall that was exposed was impressive. The walls were clearly carefully constructed by whoever built them, with careful attention paid to creating a neat interior wall face. This indicates that this was a well-built and long-lived structure or house rather than a more basic shelter or farm building. The wall was also around 0.75m wide and would have stood at least 1.6 metres high. It would have no doubt been capable of withstanding even the harshest of winter storms. Unfortunately, no artefacts were recovered which meant that the date of the structure remains a mystery. Who knows, maybe all of the artefacts were destroyed by the highly acidic ‘soils’ kindly distributed by the gannets.

Although the dating of Grassholm’s archaeology remains problematic, it is clear through the work undertaken by CHERISH and past researchers just how archaeologically rich the Island is. Whether the structures and field walls are hundreds, or thousands of years old, it is clear that people were attracted to the island and probably even lived there at points throughout history. Whilst not all the questions could be answered through undertaking this work it is important that the island continues to be monitored for archaeology uncovered by vegetation erosion to continue piecing together the island’s elusive history. For a place so remote and isolated, there is no doubt that it would have played a significant role in many people’s lives spanning generations and time periods.