a. Ynys-y-Fydlyn is a distinctive promontory but no cross-banks suggesting a defensive function were noted during field work. The neck of the promontory is fractured leaving the seaward end inaccessible, while the landward end is now under forestry and is also largely inaccessible.

David Leighton, RCAHMW, 1994

b. There is a distinct bank cutting across the E side of the island from NE - SW., about 20m long, 0.5m high and 0.75m wide, cut through by a footpath near its NE end. Though artificial it is a rather slight bank and as Frances Lynch has pointed out in an unpublished document: "a rather pointless construction". However it can be seen as part of a 'defence' even if it served only as a token barrier. This part of the island is now separated from the rest of the island (on which there is a single hut circle, NPRN 422209), by a deep unjumpable chasm, though both parts of Ynys y Fydlyn are approachable at low tide. Very unlikely the chasm has formed since the building of the hut or the defensive bank, but a natural arch spanning the gap could have fallen in during this time. The bank would then make more sense as a 'defensive' feature.

John Latham RCAHMW 8 August 2017
Source: Unpublished report for the National Trust, Mynachdy 1991, John Latham.

Ynys-y-Fydlyn, as part of Carmel Head, has been monitored as part of the CHERISH project, due to being at risk from natural processes exacerbated by climate change. CHERISH (Climate, Heritage and Environments of Reefs, Islands and Headlands) is an EU-funded Wales-Ireland project (2017-2022) 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. Work included aerial survey in 2016 and photographic survey in 2018.

H. Genders Boyd, CHERISH, April 2022