|Sovereign state||United Kingdom|
|Fire||Mid and West Wales|
Trefasser (variations: Tref-Asser, or Trêf Asser, or Asserton; translation: "town" of "Asser") is a hamlet, located to the west of Fishguard and south of Pwll Deri in western Wales. Historically, it is part of the parish of Llanwnda. It lies on the coast of St George's Channel within the Pembrokeshire Coast National Park. A stream named Cledde Goch runs close by.
There are opposing views as to from whom the name derives. One possibility is that it is the namesake of Bishop Asser, a friend and biographer of King Alfred in the 9th century. Another possibility is that it is named for Asser's nephew, Asser Meneventsis, as Trefasser is said to be his birthplace. Meneventsis was a Benedictine monk, as well as scribe and chancellor to Asser.
A tumulus named Castell Poeth ("the Hot Castle") is located nearby. It is an exploratory castelet with an occasional beacon. Described as a ditched, raised enclosure, oval in shape, and measuring 30 m (98 ft) by 60 m (200 ft) across, it has an attached second oval measuring 46 m (151 ft) by 54 m (177 ft).
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- Wiles, J. (07.04.04). "CASTELL POETH". Royal Commission on the Ancient and Historical Monuments of Wales. Retrieved 4 October 2010. Check date values in: