In 2017 Dinas Dinlle became the focus of new archaeological and palynological research and survey work as part of the 2017-2023 EU-funded CHERISH Ireland-Wales project. In August 2019 the Gwynedd Archaeological Trust was funded by CHERISH to run a 3-week evaluation excavation involving local volunteers, targetting anomolies identified in a CHERISh funded Magnetometry survey. In 2021, further excavation was undertaken by Gwynedd Archaeological Trust (GAT) in partnership with Cadw, the CHERISH project, the National Trust, Bangor University and the Welsh Areas of Outstanding National Beauty (Sustainable Development Fund).

These excavations provided evidence for a substantial roundhouse, with an external diameter of 13.6m (internal 8m) and 2.5m thick walls, some of the most substantial known in Wales or England, and the remains of a slate slab floor, suggesting a high-status building. Its size suggests that it could potentially be the central house of the hillfort. Radiocarbon dating of occupation deposits inside returned late Iron Age to late Roman dates. Roman pottery was found inside (samian ware from Gaul and black burnished ware) suggesting Romano-British occupation. The excavation showed that the roundhouse walls collapsed to the south and were subsequently sealed by deposits of windblown sand. There are historical accounts of storms causing extensive sand inundation (for example on Anglesey in 1331) and luminescence analysis on nearby dune systems has found evidence for significant sand inundations in the area. It is likely that the hillfort at Dinas Dinlle was inundated with windblown sand at various times during major storm events. 

There are marked parallels in the plan of the building with the West Area roundhouse (Building S, Phase 1b) of the Ty Mawr hut settlement, Holyhead, excavated 1978-82 (see Smith 1985, Figure 6).

Following further excavation in 2022 the footing of the roundhouse was consolidated and preserved by the National Trust. 

CHERISH (Climate, Heritage and Environments of Reefs, Islands and Headlands) is an EU-funded Wales-Ireland project (2017-2022) 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.

References: 

• Hopewell, D. 2018. Geophysical Survey at Dinas Dinlle Hillfort, Llandwrog, Gwynedd. GAT Report No. 1434. http://www.walesher1974.org/her/groups/GAT/media/GAT_Reports/GATreport_1434_compressed.pdf  

• 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 2022. GAT Report No. 1628. http://www.walesher1974.org/her/groups/GAT/media/GAT_Reports/GATReport_1628_compressed.pdf
• 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. http://www.walesher1974.org/her/groups/GAT/media/GAT_Reports/GATreport_1582_compressed.pdf  
• Ranwell, D.S. 1958. Movement of vegetated sand dunes at Newborough Warren, Anglesey. Journal of
• Ecology, 46, 83-100
• Smith, C. 1985. Excavations at the Ty Mawr Hut-circles, Holyhead, Angelsey, Part II. Archaeologia Cambrensis, Vol. CXXXIV. 11-52

H. Genders Boyd, RCAHMW for the CHERISH Project, February 2022.