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Castell Bach, Cwmtydu

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Castell Bach is one of the few coastal forts of Ceredigion and occupies a spectacular but secluded location. Questions remains about why it was built in this particular location and to what extent coastal erosion has reduced the size of the fort seen today. Descending from the high coastal plateau towards Castell Bach a restricted saddle of level ground is encountered at the base of a great `bowl’ in the coastal slopes. The triple ramparts of the fort enclose this entire saddle hemmed in on the south and east sides by steep scarps, on the north by 20 metre high coastal cliffs and to the west by a narrow inlet. Dominating the view, and the coastal inlet, is a freestanding coastal stack which appears to have artificial platforms cut into its pointed summit. Was this originally part of the fort before it was cut away by coastal erosion or was this always separate, perhaps reached by a now eroded land bridge between fort and stack?

The inner fort and outer annex:

The bivallate (double-ditched) inner fort currently encloses a quarter of a hectare defined by two close-set ramparts each with an outer ditch; a third rampart and outer ditch are widely spaced some 100m to the east. The whole presently encloses 1.48ha, but may have enclosed nearly 2 hectares before coastal erosion cut away the west side. No artificial defences were required on the south side where the ground rises in a steep scarp.

The bivallate defences of the inner fort swing around to enclose the north-west part of the coastal saddle. The inner rampart stands around 7m wide and 2m tall. The outer is half the width of the inner but stands slightly taller in places and is reveted on its outer eastern face with substantial stone blocks. The intervening ditch, about a metre deep, is water-filled and fed by a spring; here and there former revetment blocks have tumbled into its base. The original main gateway was to the north near the cliff edge where a 3m gap on the inner rampart is matched by a 2.5m gap in the outer, with heightened gateway terminals albeit only standing a metre high.

Cliff erosion through the inner ramparts:

Both the inner ramparts are actively eroding on the west side, revealing a cross-section in slumping cliffs. Studies by Keith Ray for the Ceredigion Archaeological Survey in the 1980s and more recently by the National Trust, suggested that the inner enclosure originally comprised a single inner bank and ditch, but then was remodelled when the outer bank and ditch were built; there was then a rebuild of the outer bank. Despite the appearance of severe coastal erosion, much of the northern cliff line is stable and even stepped-back from the waves. There is no reason to doubt that these are the original northern extents of the fort's defences, with the only losses found on the west side.

The third, outer, defensive bank set apart from the inner may indicate a later expansion of the site. This bank respects the modern cliff edge by ending in an inturned gateway terminal on the north side leaving a 6m outer gateway. This was clearly the original way into the fort from the east. This wide-spaced outer rampart stands about 7m wide and 2m high in places with a deep outer ditch making the defence seem more formidable. As with the inner fort, the ditch also encloses an active spring. An eroded modern cut through this rampart shows a span of 2m between inner and outer revetment walls. This great outermost enclosure to the inner fort is featureless today despite suggestions of an enclosure spotted on aerial photographs in the 1980s. The ‘enclosure’ probably derives from a series of relatively recent `herringbone? field drains dug across the center of the saddle, and visible as parchmarks on aerial photos. A third spring is sited on the cliff edge midway along the annex, walled with small stone blocks which may well be of prehistoric date. Similar walled springs can be seen on Skomer Island, Pembrokeshire. (Edited from Driver, T. 2016, 147-150).


  • Davies, J. L. 1994 in: Cardiganshire County History Volume 1, p. 248 and Figure 46 (inaccurate in detail and orientation).
  • Driver, T. 2016. The Hillforts of Cardigan Bay, Logaston Press.



Castell Bach is a baseline study site for the EU-funded Ireland-Wales CHERISH Project 2017-2021. Work on site has seen a new UAV photogrammetric survey (2018), new topographic and geophysical survey (2019), and photogrammetry (2022).

A detailed magnetometry survey was conducted over approximately 1.5 ha of rough pasture land at Castell Bach, Cwmtydu, by SUMO Services for the CHERISH Project in March 2019. The survey has recorded anomalies which reflect the inner and outer ramparts of the Scheduled promontory fort, which survive as extant earthworks. A small cluster of discrete anomalies and areas of enhanced magnetic response have been detected within the inner enclosure, and it is possible that these are a result of settlement activity. A large number of discrete, linear and amorphous areas of increased response are present in the data, all of which are of uncertain origin.

A 3D model of the site was created following the UAV photogrammetric survey in 2018 which can be accessed with the links below:



CHERISH (Climate, Heritage and Environments of Reefs, Islands and Headlands) is a European-funded project 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. The project commenced 1st January 2017 and will run for 6 years to June 2023; it will receive more than €5.9 million of European Union (EU) funds through the Ireland – Wales Co-operation Programme 2014-2020, Priority Axis 2 – Adaptation of the Irish Sea and Coastal Communities to Climate Change. 


Davies, R. 2019. Geophysical Survey Report 14719: CHERISH Ireland-Wales Project - Castell Bach, Cwmtydu, Ceredigion. SUMO Services. Unpublished.

application/postscriptGeneral Digital Donations CollectionCastell Bach, Cwmtydu; .ai version of a plan showing the inner and outer ramparts (green), ditches (brown), the isolated coastal stack and the site of the spring in the cliff face. Figure 7.23, The Hillforts of Cardigan Bay, Toby Driver.
application/pdfCHR - CHERISH Project ArchiveSumo Survey Report No 14719 "Geophysical Survey Report CHERISH Ireland-Wales Project - Castell Bach, Cwmtydu, Ceredigion" May 2019. ? Crown: CHERISH PROJECT 2019. Produced with EU funds through the Ireland Wales Co-operation Programme 2014-2020. All material made freely available through the Open Government Licence.