Has been described as a Rejected Timber Castle (Other/Unknown)

There are earthwork remains

Alternative NamesSnowdon; Smardon; Sinnodune; Castell Caer Lleion; Castell Caer Seion
Historic CountryCaernarfonshire
Modern AuthorityConwy
1974 AuthorityGwynedd

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)

This site is a scheduled monument protected by law

Not Listed

The National Monument Record (Coflein) number(s)
County Historic Environment Record
OS Map Grid ReferenceSH760778
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  • King, D.J.C., 1983, Castellarium Anglicanum (London: Kraus) Vol. 1 p. 35
  • RCAHMW, 1956, A Survey and Inventory of the Ancient Monuments of Caernarvonshire Vol. 1: East (HMSO) p. 70-2 online copy


  • Toulmin-Smith, Lucy (ed), 1906, Leland's Itinerary in Wales  (Bell and Sons; London) p. 84 online copy