1. Summary

Llyn Cerrig-bach votive lake, dating from the Celtic Iron Age in the final centuries BC, is a small lake on the western edge of Ynys Môn /Anglesey. It is part of a wider coastal wetland landscape of small lakes, bogs, rock outcrops and islets. The wetland landscape was first seriously impinged upon in 1942 with the construction of the wartime airfield (now RAF Valley) just to the south, built on levelled sand dunes. However it was not until airfield expansion in 1943 when peat was systematically excavated from the wetland margins to place over and stabilise the loose sand – then causing havoc by blowing into aircraft engines – that the treasures of Llyn Cerrig-bach were discovered. Indeed, the peat from several lakes had been fully excavated and spread across the intervening spaces of the runways, and was in the process of being harrowed and seeded, when the first artefacts were collected by the workmen on site. The source of the finds was traced back to only one lake, Llyn Cerrig Bach; the finds achieved wider attention when brought to the attention of Cyril Fox at the National Museum of Wales.

The finds at Llyn Cerrig Bach are the most important British example of a phenomenon well known on the Continent and described by Caesar - a sacred lake where quantities of prestige artefacts and weaponry  were thrown by the Iron Age Celts as offerings to their gods.

The finds are primarily military and included eleven swords, eight spearheads and parts of a parade shield. Equipment from several chariots were also present, both the harness and parts of the structure. Up to 22 chariots can be recognised from the wheels discovered. The dates of the finds are also of interest. Some of the swords are of types current in the 2nd century BC, others are of later designs, but nothing later than AD 60 can be identified. This suggests that the lake developed its importance in the latter half of the Iron Age, with the Roman invasion of Anglesey in AD 60 perhaps finally curtailing the deposition of metalwork at this location.

2. Summary from MacDonald's study of the artefact assemblage, 2007

'The Llyn Cerrig Bach assemblage is one of the most important collections of La Tene metalwork discovered in the British Isles. It came to light during construction work in 1943 at RAF Valley in north-west Anglesey when it was disturbed during the extraction of peat from the Cors yr Ynys bog located on the southern margin of Llyn Cerrig Bach. A total of 180 iron and copper allow artefacts are known to have been recovered from the airfield, of which all but four are now in the collection of the National Museum of Wales (Macdonald 2007, 1).

3. Summary from Driver, describing votive lakes in Wales, 2023

‘… The Iron Age landscape was alive with places of religious and sacred significance. The hoarding of prestige metalwork including swords, weapons and valuable metalworker’s scrap, had been taking place since the Bronze Age… Into the Iron Age across Britain, Ireland and wider continental Europe, the conspicuous deposition of metalwork became ever more associated with watery places; the bends of major rivers, natural springs, the dark waters of upland lakes and the dangerous pools of mist-shrouded bogs..

… Llyn Cerrig Bach on Anglesey [was] discovered during airfield construction in 1943, when peat was mechanically dragged out of the wetland to stabilise coastal sand dunes around the newly-built runways. A large hoard of metalwork dating to the last three centuries before the Roman conquest included swords, spears, shield and chariot fittings. The location of the finds suggests that they were thrown into the dark waters from a rock platform on the lake edge. The position of the lake, very close to the western seaways off Anglesey, may suggest that this intensely-used sacred location was known far and wide to seafaring visitors (Driver 2023, 89-90)’.

4. Investigations by Operation Nightingale, 2024-25

In 2024, a team of recovering military personnel from Operation Nightingale, led by Richard Osgood of the Defence Infrastructure Organisation, returned to RAF Valley to carry out metal detector surveys under controlled conditions to assess if further Iron Age metalwork survived undiscovered in the areas between the runways, where peat from the lake had originally been spread. Following two days of survey, a bridle bit and terret ring (chariot rein guide) were recovered, and declared Treasure by Amgueddfa Cymru/National Museum Wales.

5. The finds from Llyn Cerrig-bach are displayed from 2018 in the refurbished galleries of St Fagans National History Museum. Some finds and reproduction finds are also on display in Oriel Môn, Llangefni, Anglesey. There is also a commemorative plaque and interpretation panel by the public road which passes the lake.

T. Driver, RCAHMW, January 2025

Main sources:

Driver, T. 2023. The Hillforts of Iron Age Wales. Logaston Press.

Fox, C. 1946. A Find of the Early Iron Age from Llyn Cerrig Bach, Anglesey. National Museum of Wales.

Lynch, F. 1991. Prehistoric Anglesey. Second Edition. The Anglesey Antiquarian Society. 285-315

Lynch, F. 1995. A Guide to Ancient and Historic Gwynedd, Cadw/HMSO

Macdonald, P. 2007. Llyn Cerrig Bach. A study of the copper alloy artefacts from the insular La Tene assemblage. University of Wales Press. Cardiff

Steele, P. 2012. Llyn Cerrig Bach, Treasure from the Iron Age. Oriel Ynys Mon/Llyfrau Magma. Llangefni.

Online sources:

Feature by Christopher Catling, 2016, from Current Archaeology: https://the-past.com/feature/the-riddle-of-the-lake-llyn-cerrig-bach-and-iron-age-anglesey/

Cadw comic guide to ‘Llyn Cerrig Bach: Links Through Time’ by John Swogger: https://cadw.gov.wales/sites/default/files/2019-05/150731llyncerrigbachcomic-en.pdf