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Dinas Dinlle Hillfort, Llandwrog

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Map ReferenceSH45NW
Grid ReferenceSH4370056350
Unitary (Local) AuthorityGwynedd
Old CountyCaernarfonshire
PeriodIron Age

1. 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 the 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 approx. 230m north-south by 145m east-west and would originally have enclosed approx. 4 hectares were it not for the severe erosion on the western (coastal) side of the hill which 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 we calculate 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.

Little is known about the monument. It is thought to be later prehistoric (Iron Age) in date but chance finds of Roman coins (of Gallienus, the Tetrici, Carausius and Allectus (253-296)), an intaglio (a carved gemstone worn in a ring) representing Victory with a trophy (known as the Cors y Gedol Intaglio (Arch Camb. 1872, 268-9)) and pottery suggest occupation in the Roman period. There is a possibility that the prominent, squarish stone mound inside the fort is the remains of a building or tower; could it be a Roman pharos or lighthouse? Early medieval occupation of this prominent site is also very likely; Dinas Dinlle takes its name from one of the Welsh legends of the Mabinogi and the story of Math mab Mathonwy and Lleu Llaw Gyffes, who gave his name to the hillfort Dinlle ('din' in old Welsh meaning fort and 'Lle' short for Lleu).

In 2017 the hillfort became the focus of new archaeological and palynological research and survey work as part of the 2017-2021 EU-funded CHERISH Ireland-Wales project. The eroded hillfort was selected as a study site and in 2017-18 saw new geophysical survey carried out by the Gwynedd Archaeological Trust, new topographic (GNSS), laser and photogrammetric survey by the Royal Commission and new laser scanning and drone photogrammetry in 2018. Survey work has extended to encompass the southern slopes beyond the hillfort defences where the geophysical survey identified the remains of historic farms depicted on the Tithe Award Survey, but also earlier traces of probable prehistoric fields and boundaries.

The first excavations on the fort were conducted in 2019 by the EU-funded CHERISH Project. In June 2019 cliff-face excavation and sampling was carried out by CHERISH staff from the Royal Commission and Aberystwyth University. Between 5th-23rd August 2019 the Gwynedd Archaeological Trust was funded by CHERISH to run a 3 week evaluation excavation involving local volunteers.

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:



T. Driver, L. Barker, D. Hunt, RCAHMW for the CHERISH Project, 2019.

2. The site is on a 30m high hill of glacial drift on the western edge of the Caernarfonshire coastal plain. This natural hill has been adapted and reinforced in the typical style of an Iron Age Hillfort with defensive central area surrounded by banks and ditches. The fortifications survive on three sides only today, the west side has been eroded away possibly during the last 100 years or so by the sea. Formerly the site may well have stood well inland. Alternatively the glacial hill may have been a coastal prominence with sea on three sides. It has a history in that it has been commented on as a site since at least the mid C18th and there are a number of references to it as a 'Camp' in the mid C19th notably in Arch Camb 1846 where there is also a fine illustration of the site from the east. It is a lone survival in the area and there are no other Hillforts nearby given the topography any scope to build one. The Hillfort on the summit of Garn Boduan is possibly the nearest similar site. It is a fine survivor but is very seriously threatened by sea erosion. This erosion has continued and has been noted for some time and its progress has been plotted from available data. It will no doubt be accentuated by sea level rise / climate change but he main threat is simply wave and wind action at present. The site exhibits not only fine surviving defences but also due to the sea erosion and a deep layer of wind blown sand some of its archaeological horizons. From the result of footpath and animal erosion some detail of its construction and its entrance features have been revealed. The volatile state of its preservation presents opportunities for archaeological investigation and better understanding of the site. The interior has possibly some buried and surviving features revealed by geophysics and there are opportunities also for further investigation and 'test-pitting'. There are several notable finds from the site including pottery coarse wares of the mid C3rd AD and coins from the same period, possibly indicating re-use during the Roman occupation.
John Latham RCAHMW 1 November 2016

(Anon) 1872. The Cors y Gedol [Dinas Dinlle] Intaglio. Archaeologia Cambrensis Vol. III, Fourth Series, p. 268-9.
Hopwell, D. 2018. Geophysical Survey at Dinas Dinlle Hillfort, Llandwrog, Gwynedd. Gwynedd Archaeological Trust Report No. 1434 (Unpublished).
RCAHMW (M) 1960. (1211) Dinas Dinlle, Llandwrog. An Inventory of the Ancient Monuments in Caernarvonshire, Volume II: Central. Pp. 189-191 & Plate 3.


application/pdfGeneral Digital Donations CollectionDigital survey depiction from a National Trust survey of Dinas Dinlle Hillfort, carried out by The Muckle Partnership, 08/2003-04/2004, showing the contour data.
application/pdfGeneral Digital Donations CollectionDigital survey depiction from a National Trust survey of Dinas Dinlle Hillfort, carried out by The Muckle Partnership, 08/2003-04/2004, showing the erosion edge.
application/pdfGAT - Gwynedd Archaeological Trust ReportsGwynedd Archaeological Trust Report relating to Dinas Dinlle Hillfort Llandwrog. Project No: G2118. Report No: 847.
application/pdfRCAHMW ExhibitionsExhibition panel entitled Ysblander Eryri a'r Cyffiniau, produced by RCAHMW for the National Eisteddfod 2005.
application/pdfRCAHMW ExhibitionsBilingual exhibition panel entitled Safloedd a Thirweddau - Sir Gaernarfon. Site and Landscapes - Caernarfonshire, produced by RCAHMW for the Royal Welsh Show, 2011.