Ancient Monuments

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Three Palmerstonian Gun Batteries, Flat Holm

A Scheduled Monument in Sully and Lavernock (Sili a Larnog), Vale of Glamorgan (Bro Morgannwg)

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Latitude: 51.3784 / 51°22'42"N

Longitude: -3.121 / 3°7'15"W

OS Eastings: 322077

OS Northings: 164969

OS Grid: ST220649

Mapcode National: GBR J0.SHMV

Mapcode Global: VH6FT.VMF5

Entry Name: Three Palmerstonian Gun Batteries, Flat Holm

Scheduled Date: 23 March 1974

Source: Cadw

Source ID: 3384

Cadw Legacy ID: GM351

Schedule Class: Defence

Category: Battery

Period: Post Medieval/Modern

County: Vale of Glamorgan (Bro Morgannwg)

Community: Sully and Lavernock (Sili a Larnog)

Traditional County: Somerset


The monument comprises the remains of a coastal battery together with associated structures dating from the 19th century. The gun batteries are situated around the periphery of the small island of Flat Holm in the middle of the Bristol Channel.

Flat Holm was first fortified in the 1860's as part of Lord Palmerston's defences for the Bristol Channel, against possible invasion by the French Navy of Napoleon III. Four batteries were built on the island:

A - Castle Rock Battery - This battery stands at the northernmost tip of the island on the cliff top. It consists of three stone-lined circular gun emplacements open to the sky, with a flat-topped mound c. 2.5m high built up around them. There is an entrance passage from the south with a stone lined lower passage leading to an area on the east side of the mound of underground rooms and passages - all built of stone. At the northern end is a room with a concrete roof. Parts of the guns are lying in the gun batteries.

B - Lighthouse Battery - This battery is situated at the southern end of the island - in the south-east corner near the lighthouse. It is a single battery consisting of a stone-lined pit 5m in diameter with a mound built up around it. On the rim of the mound on the east side a complete gun is lying half buried. It is c. 3.5m long and weighs 6-7 tons. On the west side there is an arched doorway into the pit with an open passage through the mound to it.

C - Lighthouse Battery - This battery is situated at the southern end of the island near the lighthouse (to the west of item B). It consists of two gun emplacements similar to item (b). These are reached from an open passage c. 2.5m deep in the mound surrounding them. The westernmost one has a second world war Nissen hut in the middle of it. There are two guns lying on the ground here, both complete and in good condition. North of the gun emplacements but still within the mound is an underground armoury, entered on its west side from the open passage.

D - Farmhouse Battery - This battery is situated on the west side of the island, northwest of the farmhouse. It consists of a flat-topped mound c. 2.5m high with two gun emplacements and storerooms in it. The emplacements are similar to others. The northern one has a concrete roof and is used as a store room. The southern one is open. Between the two store rooms, reached from the northern emplacement there is a tunnel on the east side which has a stone-lined entrance. Part of a gun remains here.

The monument is of national importance for its potential to enhance our knowledge of 19th century coastal defence practices. The monument is well preserved and is an important relic of actions taken against the perceived threat of naval attack in and above the Bristol Channel. It retains significant archaeological potential, with a strong probability of the presence of associated archaeological features and deposits. The importance of the monument is further enhanced by the group value formed by the association of the individual structures within the overall defensive scheme. A battery may be part of a larger cluster of anti-invasion defences and their importance can further enhanced by their group value.

The scheduled area comprises the remains described and areas around them within which related evidence may be expected to survive.

Source: Cadw

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