Ancient Monuments

History on the Ground

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Dinas Dinlle Seagull Trench

A Scheduled Monument in Llandwrog, Gwynedd

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Latitude: 53.0831 / 53°4'59"N

Longitude: -4.3353 / 4°20'7"W

OS Eastings: 243679

OS Northings: 356537

OS Grid: SH436565

Mapcode National: GBR 5F.9WW5

Mapcode Global: WH43L.CRSS

Entry Name: Dinas Dinlle Seagull Trench

Scheduled Date: 8 June 2006

Source: Cadw

Source ID: 1168

Cadw Legacy ID: CN396

Schedule Class: Defence

Category: Seagull Trench

Period: Post Medieval/Modern

County: Gwynedd

Community: Llandwrog

Traditional County: Caernarfonshire


The monument comprises a seagull trench, a partially buried defensive structure dating to World War II (AD 1939-45). It is embedded into the bottom of a steep N facing slope in an enclosed field of pasture. The structure is mostly subterranean and consists of five compartments with only a concrete roof and ten embrasures visible externally. The seagull trench measures 22.4m long, c.4m deep and c.2.5m tall. It is aligned ENE-WSW. An entrance and associated tunnel lie to the S. Its name is derived from its shape on plan which resembles a bird.

The monument is of national importance for its potential to enhance our knowledge of World War II defensive practices. Further, this example is a rare occurrence of this site type in Wales. The monument is well preserved and is an important relic of the perimeter defences of the former RAF station at Llandwrog. It retains significant archaeological potential, with a strong probability of the presence of associated archaeological features and deposits.

Source: Cadw

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