The comprehensive gazetteer and bibliography of the medieval castles, fortifications and palaces of England, Wales, the Islands.
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Also known as, or recorded in historical documents as;
Snowdon; Smardon; Sinnodune; Castell Caer Lleion; Castell Caer Seion

In the community of Conwy.
In the historic county of Caernarfonshire.
Modern authority of Conwy.
Preserved county of Gwynedd.

OS Map Grid Reference: SH76037783
Latitude 53.28258° Longitude -3.86167°

Sinadon has been described as a Timber Castle but is rejected as such.

There are earthwork remains.

This site is a scheduled monument protected by law.


Castle cited by Leland as 'Sinnodune a Mile from Conwey' is, in fact, Castell Caer Lleion which is pre Roman Iron Age.

Hillfort on Conway Mountain (Mynydd y Dref), also known as Castell Caer Seion or Lleion. The summit of a ridge of rhyolite is enclosed by a single rampart, with more complex works protecting a smaller fortified area at the W end. Within the fort 58 round hut foundations are visible as levelled platforms, including 7 in the smaller enclosure. The large enclosure also contains a rectangular levelled platform, on the N slopes 430ft NNE from the main entrance; 600ft NE from the entrance is a circular pit of about 4ft diameter with a trench leading into it from the NE - in plan resembling a corn-drying kiln. There are possible traces of others. The detailed structural history of the site remains open to several widely different interpretations. It appears certain that the existing remains represent two or more periods of construction, during at least one of which both the enclosures were occupied together, although there is no indication of direct access from one to the other, and indeed the small enclosure seems to have been designed to resist attack from within the large enclosure as well as from outside. The site is traditionally associated with Maelgwn, but there is no other evidence either way as to a sixth-century occupation. The main structure belongs to the pre-Roman Iron Age. (Scheduling Report)
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Sources of information, references and further reading
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The bibliography owes much to various bibliographies produced by John Kenyon for the Council for British Archaeology, the Castle Studies Group and others.
Suggestions for finding online and/or hard copies of bibliographical sources can be seen at this link.
Minor archaeological investigations, such as watching brief reports, and some other 'grey' literature is most likely to be held by H.E.R.s but is often poorly referenced and is unlikely to be recorded here, or elsewhere, but some suggestions can be found here.
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Locations derived from OS grid references and from latitude longitiude may differ by a small distance.
Further information on mapping and location can be seen at this link.
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This record last updated 05/07/2016 21:58:43