Excavating Dinas Dinlle before it falls into the sea

The plan now is to fully preserve the roundhouse and leave it open so that people may appreciate the scale of erosion that is occurring at this site.

A third season of excavation has just concluded at Dinas Dinlle, a clifftop hillfort located 12km south-west of Caernarfon (below). The work was carried out by archaeologists from Gwynedd Archaeological Trust, working in collaboration with Cadw, the National Trust, AONB Sustainable Development Fund, and CHERISH – an EU-funded project that is examining the impact of climate change on heritage sites found along the coasts of Wales and Ireland (see CA 324).

IMAGE: Gwynedd Archaeological Trust.

As we first reported in CA 356, after some initial geophysical surveys to establish the notable features of the site, two trial trenches were opened and a 13m-wide roundhouse – one of the largest ever found in Wales – with unusually thick walls (2.4m) was partially revealed. After a year interrupted by COVID-19, the team was back at the site last year to carry out a more detailed excavation of both the NNW and SSE quadrants of the roundhouse. This work established that a prominent entrance to the building was located on the eastward-facing wall. In a second trench they also discovered a corner of another roundhouse, which appears to be firmly Iron Age in date as well as a possible industrial area characterised by a metalled surface and burned sherds of Roman pottery.

IMAGE: Gwynedd Archaeological Trust.

This year, over July and the first part of August, the team then finished excavating the roundhouse, revealing it in its entirety (above). This work has confirmed that there was one primary phase of activity sometime between the 2nd and 3rd centuries AD, which was then closely followed by a second, probably brief, period of occupation that occurred soon after the first. While only a few small finds were uncovered, they included Roman coins, Black burnished ware, and some Samian ware, indicating a level of trade with the Romans – possibly from the nearby Segontium fort.

With the entryway now fully excavated, it has been shown to be an exceptionally grand one with the walls flaring out to a width of over 2.9m on either side. The floor of the entry also appears to have been paved with slate. This is a slightly unusual feature as, while this area of Wales was very close to major slate-production areas during the Romano-British period, slate appears to have mainly been used for roofing during this time. While post-excavation work will hopefully better establish the layout and use of this roundhouse, based on some of these unusual features it may have served as some sort of communal building.

The plan now is to fully preserve the roundhouse and leave it open so that people may appreciate the scale of erosion that is occurring at this site (and many other sites around the country and world) in real time. The entirety of the fort is quickly falling into the sea as a combination of water drainage and wind – exacerbated by the effects of climate change – are seeing the clifftop erode at an average rate of 0.4m per year. Over 20m of the site has been estimated to be lost already and it is predicted that within 500 years the entire site will be completely gone.

While no further work, other than the preservation of the site, is planned, there are known to be other significant archaeological features along the cliff edge and it is hoped that funding may be secured to study these before they, too, are gone forever.