The origin of this prominent earthwork mound, situated in the northeast corner of the interior of Dinas Dinlle coastal hillfort, is unknown but there is the possibility that it is the remains of a building or tower. Potential interpretations include an Early Bronze Age burial cairn/barrow pre-dating the fort, later excavated or modified; a Roman watchtower or pharos; a small medieval motte or castle tower; or a later post medieval cottage or building.

In 2017 the hillfort became the focus of new archaeological and palynological research and survey work as part of the 2017-2023 EU-funded CHERISH Ireland-Wales project (see notes section). This work included topographical and earthwork survey of the mound and two geophysical surveys – resistivity in 2019 and Ground Penetrating Radar in 2020.

The earthwork survey showed the mound to comprise two parts, a wider 22.5m diameter by 1.5m high circular mound, on top of which there is a smaller, squarer mound, 11m diameter and 0.8m high. A hole in the centre of this upper mound suggests possible antiquarian digging or an additional structure.

On 13th August 2019 the resistivity survey, undertaken by a geophysical survey subcontractor Eden Mapping and including volunteer engagement, found high resistance readings over the southern section of the mound. The high resistance could be from the compacted nature of the mound but may also infer the presence of resistive materials such as stone. The interior of the mound proved to be of average resistance, suggesting that this area could have been excavated out at some point. The results were not able to identify specific archaeological activity, but they do suggest potential for further investigation.

Wheeler (1923, 348) notes that around 1800 A quantity of Roman Coins, chiefly of Alectus, was found in a hollow in the mound in the interior area by a shoemaker. This is likely to be a reference to the mound and the potential excavation hollow. (see NPRN 800086) 

References: 

• Barker, N. (2019) Geophysical Survey, GAT ref G2608
• Griffiths, W. E., 1949, Roman Coins from Dinas Dinlle. Transactions of the Caernarvonshire Historical Society. Vol 10, pp. 1-2.
• Hopewell, D. 2021. An interim summary of the results of the excavations at Dinas Dinlle (2019 and 2021). Gwynedd Archaeological Trust. 
• 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. 
• Wheeler, R. E. M., 1923 Roman Coin Hoards in Wales. Caernarvonshir. The Bulletin of the Board of Celtic Studies. Vol 1, 348

H. Genders Boyd & Louise Barker, RCAHMW for the CHERISH Project, 2022. 

CHERISH (Climate, Heritage and Environments of Reefs, Islands and Headlands) is an EU-funded Wales-Ireland project (2017-2023) 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.  https://cherishproject.eu/en/