Historic excavation at Dinas Dinlle coastal fort reveals its deeply buried secrets


Dinas Dinlle aerial

Dinas Dinlle and its environs during the 2018 drought, viewed from the west. Crown Copyright: CHERISH AP_2018_2346.

Last week saw the end of the first ever archaeological excavation to be carried out at the hugely important and National Trust owned prehistoric coastal fort of Dinas Dinlle. Archaeologists from the European-funded CHERISH Project and Gwynedd Archaeological Trust worked for three weeks during August in an attempt to unlock some of the site’s secrets that have eluded people for centuries. Around 50 volunteers from the local community were also able to get their hands dirty uncovering the story of the fort. For many, this was their first dig where they were able to learn more about their local history as well as gaining key archaeological skills to take forward to other excavations within their local area. What they uncovered beneath the ground has added to the ever-changing story of this enigmatic site…

As the archaeologists watched the diggers strip away the turf and topsoil it became clear that all was not as expected. They were faced with tonnes of sand overlaying the archaeological layers and features. The two trenches within the interior of the fort contained the most sand and in places the first traces of archaeology did not appear until 1.5m down! For a protected monument with visible earthworks the archaeology was not expected to be so deeply buried. There were also thinner deposits of sand across the trenches in the southern field that appeared to overlie post-medieval field systems.

 Cut section of trench showing layers of soil and sand

A cut section down to the natural boulder clay. This section shows several soil horizons and layers of sand in the field to the south of the fort possibly deposited by intense storms. Crown Copyright: CHERISH.

Buried beneath the copious amounts of sand was some fantastic archaeology that exhibited clear evidence of occupation in and around the fort. The hillfort is thought to be Iron Age in origin, and previous finds also suggest Romano-British occupation, it’s fame in the Welsh legends of the Mabinogi also suggests the potential for Early Medieval occupation. A large stone-built roundhouse structure, structural debris, field boundaries and pottery sherds of different dates unearthed during the dig all point towards a site and landscape that people have lived and farmed in for generations.

Northern wall of Roundhouse uncovered by excavation

The northern wall of the roundhouse uncovered by excavation. The impressive walls appear to have been constructed from large stones to a width of 1.5m. Crown Copyright: CHERISH.

By far the most impressive discovery was the monumental stone-built roundhouse uncovered within the interior of the fort. Measuring an impressive 13m in diameter it is believed to be one of the biggest of its kind ever found in Wales and perhaps one of the most threatened by erosion anywhere in the UK. The stone walls themselves are striking, measuring over 2.4m in thickness and at least 1.5m in height, with at least two courses of stones believed to still be buried beneath the level reached by the archaeologists. Unfortunately, archaeologists were unable to reach the occupational floor layers of the structure due to time constraints, so it is hard to provide conclusive evidence for its date and function beyond the few sherds of Roman pottery found close to the walls.

Several questions have arisen from its discovery: when was it built and how does it fit in the broader story of the fort? Was it constructed in such a way to withstand severe storms, and was it abandoned due to sand inundation? These are all questions that the archaeologists and volunteers were left scratching their heads over as they watched the trenches being back-filled on the final day. With further post-excavation analysis these questions may begin to be addressed, however, further excavation may be the only way to get to the crux of the history of this structure.

 Artists reconstruction of roundhouse

A reconstruction of the partially excavated roundhouse viewed from the north. This illustration shows how it may have appeared complete with broad stone walls supporting a tall conical roof. The location of the doorway, and many other details shown, are entirely conjectural. Created by Toby Driver from the CHERISH team. Copyright: Toby Driver.

The second trench to the south of the roundhouse also revealed archaeological remains buried deep beneath sand. Several archaeological layers and features were identified and excavated, however, time proved again to be the enemy. Amongst the investigated deposits was pottery of possible Roman date, reinforcing previous interpretations that the fort was occupied in Roman times. An interesting and heavily eroded iron object was also discovered by chance at the bottom of one of the excavated sections of a small ditch. Initial thoughts point towards it possibly being some form spearhead due to its shape, but further analysis will need to be undertaken to determine its true character. The density of archaeology within the small exploratory test pits within the trench suggests huge archaeological potential at this location within the fort, with features that may be associated with additional roundhouses and other settlement features likely still preserved beneath the surface.

The excellent preservation of the stone walls of the roundhouse – and presumably other features yet to be uncovered – suggests that the initial sand deposition at the site may have been rapid, likely during periods of major storm activity. Nearby, southwest Anglesey has a well-documented history of sand inundation associated with storms during the medieval period at Newborough and Aberffraw. Work by CHERISH scientists from Aberystwyth University is ongoing to investigate the longer term record of environmental change in the area and has identified earlier phases of sand deposition in sediment cores from Llyn Coron, near Aberffraw. How Dinas Dinlle fits into this story is now the main focus for CHERISH. The team is using luminescence dating to determine when, and how quickly, the archaeological evidence was buried by sand. Samples were taken from both interior trenches (five from each) to cover the full trench depth, also focusing on the context of key finds such as the iron object described above. These will be processed over the coming months at Aberystwyth Luminescence Research Laboratory along with samples from the cliff face investigation (which we think relate largely to the glacial origin of the site). Watch this space for results…

 Professor Helen Roberts taking luminescence samples

Professor Helen Roberts from Aberystwyth University taking Luminescence samples from a section adjacent to the southern wall of the roundhouse. These samples will hopefully provide dates for the sand inundation of the structure. Copyright: CHERISH.

Further work is also underway studying the past environments in and around the fort where sediment cores have been taken for pollen, diatom and chemical analysis to provide a timeline for environmental change. Initial radiocarbon dates from the base of cores indicate these cores cover the last c. 3,000 years. Another important part of the story – the sand dunes at Morfa Dinlle immediately to the north – will be investigated later this year. Here, CHERISH is teaming up with colleagues from Birkbeck University of London, who have previously undertaken geophysical surveys, to investigate the timing of the development of the beach ridges and dune system. A more complete understanding of the wider landscape will help us to interpret the archaeological evidence at Dinas Dinlle – and the importance of environmental change and past storminess in its history.

 Luminescence sampling

Helen extracting a luminesence sample from a ditch features within the interior of the fort. The sample was taken near to where an interesting iron object was found. Photo: Sarah Davies.

There was also a lot to see in the field to the south of the fort where trenches were dug to test several anomalies identified by a geophysical survey carried out in 2018. Many of the features identified through this survey align with boundaries that are visible on 1849 tithe mapping which shows land divisions and key structures extant at the time of its creation. However, there were numerous features which appeared not to respect the 1849 field boundaries, possibly indicative of earlier features which may be related to the use and occupation of the fort. Many of the features uncovered were confirmed to be post-medieval in date through the presence of large amount of Buckley Ware pottery which was produced in Buckley, Flintshire in the medieval period through to the twentieth century. An area of dense stone debris was uncovered in the southern-most trench which possibly relates to a structure visible on the tithe mapping. In the dying days of the excavation Roman pottery was also discovered in one of the features, possibly extending Roman activity to outside of the fort. This poses the question whether the land surrounding the fort was settled and cultivated during this period. Further investigation was again curtailed by the lack of time, but it is possible that deeper down beneath more sand there is evidence for prehistoric and Roman occupation.

 CHERISH Volunteers and staff

Smiling volunteers and staff! This project would not have been possible without the fantastic group of volunteers that worked through the wind and rain to uncover the archaeology. Photo: Toby Driver.

This inaugural excavation at Dinas Dinlle has provided a tiny snapshot of the exciting history of the site and has shown it has some deeply buried secrets, which may not be given up easily! As the archaeologists looked on while the trenches they had worked tirelessly in were backfilled, they were able to reflect on what had been uncovered during the three-week excavation. Why build such a huge fort with such well-built, robust structures within it? Were the inhabitants protecting themselves from the threat of violence from neighbouring tribes or were they actually fighting a long battle against relentless winds, storms and the dynamic environment all around them? These questions may never be answered, but what is certain is that this excavation has provided a critical insight into a valuable heritage site that is currently fighting its own battles against climate change, sea-level rise and severe erosion.