Dinas Dinlle coastal hillfort is owned by the National Trust. It is set on a hill of glacial drift sediments (specifically a thrust-block moraine) overlooking the sea and Caernarfonshire coastal plain. The hillfort and Second World War seagull trench (NPRN 270526) on the northern slopes of the fort are protected as Scheduled Monuments by Cadw and the hill is a Site of Special Scientific Interest (SSSI), designated for the importance of its glacial sediments, clearly seen in the exposed sections of till, sand and gravel in the cliff face.

The hillfort, a polygonal defended enclosure with a high inner rampart, and outer terraced rampart divided by a deep ditch, measures approximately 230m north-south by 145m east-west and would originally have enclosed approximately 4 hectares. Severe erosion on the western (coastal) side of the hill has removed around a fifth of the monument. Early maps, and the curve of the surviving hillfort defences, suggest that it was once entirely enclosed but today the majority of the western defences have been lost to the sea following years of erosion. It is difficult to say precisely how much of the hillfort has been lost since its construction, but measuring cliff top positions using Ordnance Survey mapping, it has been calculated that between 20 to 40 metres of the western side has been lost since 1900. Assuming that future rates of erosion will be higher than those observed over the last 117 years, due to climate change, Dinas Dinlle could be completely lost within 500 years. The 130m long strip of the interior of the fort above the cliff is under immediate threat.

The archaeological remains within the hillfort, including roundhouses, are particularly well-preserved, mostly as a result of it having been protected by a metre of wind-blown sand, which began to bury the site c. 1100 years before present. Excavation evidence and radiocarbon dates from the roundhouses indicate Iron Age construction, with continued occupation into the Roman period. Artefactual finds include Black Burnished ware, red Samian ware, Roman coins, and a stray find of an intaglio.

The prominent, squarish stone mound inside the fort (NPRN 703006) is of unknown origin. It may be a burial mound pre-dating the hillfort, the remains of a building or tower, evidence of recent activity, or a Roman pharos (lighthouse).

Early medieval occupation of this prominent site is a possibility, as Dinas Dinlle takes its name from one of the legendary figures of the Mabinogion: Lleu Llaw Gyffes ('din' in old Welsh meaning fort and 'Lle' short for Lleu). There is evidence for a longevity of occupation across the area: Neolithic remains have been found immediately south of the hillfort (NPRN 703005) along with medieval, post-medieval (NPRN 703004) and modern agricultural activity (NPRN 703003) at the site. In the early 20th century the hillfort was incorporated into a golf course (NPRN 703010) and was later used in the defence network surrounding RAF Llandwrog during the Second World War.

In 2017 the eroding hillfort and surrounding area became the focus of new archaeological and palynological research and survey work as part of the 2017-2023 EU-funded CHERISH climate change and coastal heritage project. Over the course of the project several phases of work were undertaken to record the archaeological remains and provide accurate baseline datasets to be used to quantify erosional processes happening at the site over the course of the project and beyond. The following provides an overview of both work carried out by CHERISH staff from RCAHMW and Aberystwyth University and work commissioned and funded by the project.

CHERISH (Climate, Heritage and Environments of Reefs, Islands and Headlands) was a European-funded project led by the Royal Commission on the Ancient and Historical Monuments of Wales, in partnership with the Discovery Programme: Centre for Archaeology and Innovation Ireland, Aberystwyth University: Department of Geography and Earth Sciences and Geological Survey, Ireland. The project commenced January 2017 and ran for 6 years to June 2023; it received more than €5.9 million of European Union (EU) funds through the Ireland – Wales Co-operation Programme 2014-2020, Priority Axis 2 – Adaptation of the Irish Sea and Coastal Communities to Climate Change.

 

Timeline of archaeological investigation at Dinas Dinlle (see references, resources and archive for details)

1993

• Coastal Zone Assessment for Wales: this study highlighted concerns surrounding the amount of the monument that has been lost to erosion and suggested work that should be carried out in advance of further loss (Riley & Smith 1993).

2004

• An analytical earthwork survey was carried out by The Muckle Partnership on behalf of The National Trust in 2004.
• GAT undertook a Gradiometer Survey of the interior of the enclosure as part of the Cadw-funded Prehistoric Defended Enclosures in northwest Wales project .

2005

• Gwynedd Archaeological Trust (GAT) carried out studies of hillforts and defended enclosures in northwest Wales on behalf of Cadw. Dinas Dinlle was included in the 2004-2005 Prehistoric Defended Enclosure Survey (Smith 2005).

2008

• GAT carried out studies of Iron Age settlements in northwest Wales on behalf of Cadw. Dinas Dinlle was included in the 2008 Iron Age Settlements in Wales study (Smith 2008).

2009-2010

• Two small watching briefs were carried out in 2009 and 2010 (Brooks & Smith 2009; Evans & Jones 2010) during work to replace the footpath and fencing, both of which had been affected by erosion. Both surveys failed to identify archaeological remains beyond modern imported deposits.

2011

• In 2011 the Royal Commission and Bangor University collaborated on a basic 3D animation and reconstruction of the hillfort as part of a project called Peoples Collection Wales.

2012

• In December 2012 a Royal Commission aerial photographic survey, in low light, revealed very low earthworks within the interior on the hillfort (published in Archaeology in Wales 52, 168-9).

2017 onwards

• Aerial survey was undertaken periodically from the beginning of the CHERISH Project in 2017 to obtain structure from motion imagery.

2017 -18

• The first stage of ground-based work completed at the site was a new earthwork/topographic survey carried out with the intention of building and improving on the Muckle survey of 2004. This work was carried out by CHERISH staff from RCAHMW using a Global Navigation Satellite System (GNSS). All visible archaeological features along with evidence of terrestrial erosion were surveyed. The eroding coastal edge was not surveyed on this occasion due to health and safety concerns. This data was obtained through Unmanned Aerial Vehicle (UAV) and laser scan surveys.

November 2017 and May 2018

• A magnetometry survey was carried out by GAT on the hillfort and southern field over November 2017 and May 2018.

• In May 2018 CHERISH staff from Aberystwyth University’s (AU) Department of Geography and Earth Sciences carried out some prospective paleoenvironmental sampling of the wider landscape. A 1.3m core retrieved (with a Russian corer) from NGR SH 44454 56573 was taken to test environmental potential within the surrounding wetlands. The basal date from this core was 2770 14C years BP. XRF elemental data was also collected from this core allowing for a rough pollen profile to be produced. However, it is thought that this may not produce a very reliable result due to poor preservation in the area. 

2018

• An aerial photogrammetric survey was carried out by UAV in June 2018, to provide a complete metric dataset of the whole monument, including the eroding cliff face.

• A new laser scan survey of the eroding cliff face was undertaken in June 2018 to establish a highly accurate baseline dataset to be used in future monitoring. During scanning, the CHERISH team also noted and recorded a small area of exposed peat deposits in the intertidal zone to the west of the fort [NPRN 524738 SH 4352 5623] that helps provide us with a greater understanding of the environment prior to the construction of the hillfort. The peat deposits date to the Mesolithic and confirm that a brackish-freshwater deltaic environment existed here at the time, with the sea around 1km west of its present-day position. The location of the peat also provides us with a maximum extent of the glacial mound upon which the hillfort is situated.

2019 

• In February 2019 paleoenvironmental sampling of the wider landscape was undertaken by AU. A 2.25m sediment core was taken from an area of scrub woodland about 600m to the east of Dinas Dinlle with the kind permission of Llyr Ellis. 
• In February 2019 an aerial photogrammetric survey was carried out by UAV to provide a comparable dataset to June 2018. This data will be used to assess erosion that occurred between the two surveys.
• In June 2019 a rope access excavation of the cliff-face was undertaken. It comprised 2 areas along the eroding cliff face of the fort. Full detailed recording of all visible features, soils and deposits within the investigation areas was carried out. The section was recorded digitally using UAV photography and photogrammetry used to create a scaled and georeferenced orthomosaic able to be transcribed during the post-excavation stage. Due to a lack of datable artefacts Optical Stimulated Luminescence (OSL) samples were taken from a selection of deposits to provide chronology and likely dates of deposition. A transect of eight cores were also extracted across the southern defences of the hillfort, in an area directly adjacent to the collapsed and slumped defences. Core locations were recorded using GNSS and were retained for further analysis and to ascertain potential for radiocarbon and luminescence dating, and geochemical analysis.
• In August 2019 a resistivity survey was undertaken by Eden Mapping of the circular (‘enigmatic’) mound, ramparts and the southern field. Report: Nigel Barker (2019) Geophysical Survey, Eden Mapping Report No. GAT-19-DIN.
• In August 2019 an evaluation excavation was undertaken by GAT, commissioned by CHERISH, to investigate several anomalies identified by the 2018 Geophysical survey (Lynes et al 2019). Evaluation trenches were positioned both within the interior of the fort and the southern field. Several archaeological features were identified within the interior including evidence of a large stone-built roundhouse and several small negative features such as pits and a small ditch. Little in the way of prehistoric archaeology was found but numerous post Medieval field boundaries were identified and recorded. OSL dating was carried out in both trenches within the interior of the fort. 
• In October 2019 Ground Penetrating Radar (GPR) survey was undertaken by SUMO Geophysics on behalf of CHERISH (Udyrysz-Kraweć & Wajzer (2020) SUMO Survey Report 16438).
• At the beginning of October 2019, the CHERISH Project excavated 12 trenches through the beach-ridge system at Morfa Dinlle to confirm their composition and takes samples for OSL dating to provide a robust chronology of their formation.
• In December 2019 Ground Penetrating Radar (GPR) trial survey was undertaken by Prof. Charles Bristow, Birkbeck University and CHERISH. The circular mound and a section across the east and south rrampart were surveyed.

2021

• In summer 2021 a season of excavation was carried out by Gwynedd Archaeological Trust with community volunteers, focusing on a circular structure identified by the geophysical survey on the western edge of the hillfort, therefore at risk from coastal erosion.

2022

• A further season of excavation was carried out, uncovering a large Iron Age roundhouse with evidence of continued occupation in the Roman period. This 13-metre diameter roundhouse is one of the largest ever excavated in Wales. The excavation revealed a rectangular hearth and substantial doorway paved with slate slabs. Roman coins and quernstones were amongst the artefacts recovered. The presence of red Samian ware may be indicative of trading with the nearby Roman fort at Segontium, Caernarfon. The footings of this roundhouse were consolidated by the National Trust and can now be seen onsite (NPRN 703001).

 

A 3D model of the site was created following the CHERISH project's drone survey in 2018 which can be accessed with the links below:

Cymraeg: https://skfb.ly/6Rxqp

English: https://skfb.ly/6Rxq6

 

The results of the 2017-2023 investigations has led to two new reconstruction drawings of the hillfort and excavated roundhouse, produced for CHERISH by Wessex Archaeology. An animation has also been created 20,000 Years and Counting: The Evolving Landscape of Dinas Dinlle, Gwynedd, Wales produced for CHERISH by Tree Top Films which can be accessed with the links below:

Cymraeg: https://youtu.be/fCbWbRSuchk

English: https://youtu.be/gpjgRWhynLk

 

H. Genders Boyd &  L. Barker, CHERISH, May 2023

 

In December 2021 CHERISH installed two fixed survey markers (survey nails in two prominent boulders) at the hillfort. The markers and their associated location coordinates (BNG) will enable accurate monitoring and change detection at the site going forward. Details are:

E2 Primary Station Marker - Easting: 243688.2649; Northing:356228.5588; Height: 19.3042

E6 Secondary Control Point - Easting: 243695.9868; Northing: 356373.3823; Height: 27.7681

See CHERISH Monitoring Network - DD_E2 and DD_E6 control markers Event Report: 09/12/2021 for full details including Witness Diagrams (CHERISH Survey Report No. CH/RCAHMW 37 and Data Archive RCCS28)

 

Louise Barker, CHERISH - RCAHMW, August 2023

 

References:

• Barker, L., 2020, Dinas Dinlle, Hillfort, Llandwrog, Gwynedd. An overview of CHERISH Project Investigations 2019, Archaeology in Wales 60, 29-36.

• Barker, L. and Corns, A. (Eds.), 2023, CHERISH: Sharing Our Practice. Investigating Heritage and Climate Change in Coastal and Maritime Environments. A Guide to the CHERISH Toolkit. (CHERISH/RCAHMW: Aberystwyth). https://cherishproject.eu/en/end-of-project-conference-ambition-delivery-and-legacy/

• Barker, L., Driver T., Hunt, D., Robson, P., 2021, Llandwrog, Dinas Dinlle Hillfort, Archaeology in Wales 59, 122.

• Barker, L., Hunt, D., Robson, P., Roberts, H., 2023 Dinas Dinlle Coastal Hillfort: Final Report. Assessment of exposed cliff-face features and core transect, 3-7 June 2019. (CHERISH Report No: CH/RCAHMW 38).

• Barker, N, 2019, Dinas Dinlle, Llandwrog: Geophysical Survey. (Eden Mapping Report No. GAT-19-DIN).

• Bristow, C and Barker L., 2023 Geophysical Survey (GPR trial) at Dinas Dinlle Hillfort, Llandwrog, Gwynedd. (CHERISH and Birkbeck University. CHERISH Event Report No: CH/Birkbeck- RCAHMW-AU 41).

• Brooks, I., and Smith, D., 2009, Dinas Dinlle Hillfort Footpath Watching Brief. (Engineering Archaeological Services Ltd, Unpublished Report)

• Craven, K., 2022, Coastal Terrain Model Dinas Dinlle (CHERISH Report No: CH/RCAHMW 40 prepared by Geological Survey Ireland).

• Hopewell, D., 2018, Geophysical Survey at Dinas Dinlle Hillfort, Llandwrog, Gwynedd. (GAT Report No. 1434).

• Hopewell, D. 2021. An interim summary of the results of the excavations at Dinas Dinlle (2019 and 2021). Gwynedd Archaeological Trust.

• Hopewell, D., and McGuinness N., 2022, Dinas Dinlle: Excavation of an eroding hillfort. Interim report – community excavations 2021. (GAT Report No. 1628).

• Jones, M, and Evans, R., 2010, Archaeological Watching Brief: Dinas Dinlle Hillfort, Llandwrog (GAT Report No. 847).  

• Lynes, M.S.; Ferreira, C.; Oattes, A.M.; Jones, B.; Evans, R.; McGuinness, N. and Ryan Young, C. 2021. Dines Dinlle archaeological evaluation excavation: Final Report. Project No. G2608, Report No. 1582. Historic Environment Record Event Primary Reference Number: 4547.

• McCarthy, J., 2023, CHERISH Dinas Dinlle: DEM of Difference (CHERISH Report No: CH/RCAHMW 39 prepared for CHERISH by TechWorks marine).

• Parry, I, Parry, L, Evans, R, Hopewell, D, Davidson, A, Williams, T, and Berks, T, 2012, Arfordir Coastal Heritage: Final Report (GAT Report No. 1044)

• Ranwell, D.S. 1958. Movement of vegetated sand dunes at Newborough Warren, Anglesey. Journal of Ecology, 46, 83-100

• RCAHMW, 1960, An Inventory of the Ancient Monuments in Caernarvonshire. Volume II: Central (Monument Number 1211, 190).

• Riley, H. & Smith, G. 1993. Coastal Erosion Survey: Aberdaron Bay to the Great Orme. GAT Report No. 79 published in Archaeology in Wales 52, 168-9

• Smith, G., 2005, A Survey of Prehistoric Defended Enclosures in North West Wales 2004-2005: West Conwy, Gwynedd (Arfon) & Anglesey, (GAT Report No. 580)

• Smith, G., 2008, Iron Age Settlements in Wales: Cadw Defended Enclosures Publication Hillforts and Hut Groups in North-West Wales (GAT Report No. 721)

• Udyrysz-Kraweć, M. & Wajzer, M. 2020. Geophysical Survey Report. CHERISH Ireland-Wales Project – Dinas Dinlle Hillfort, Llandwrog. (SUMO Survey Report 16438).