Ancient Monuments

History on the Ground

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Relict Seawall alongside Collister Pill Reen

A Scheduled Monument in Magor with Undy (Magwyr gyda Gwndy), Monmouthshire (Sir Fynwy)

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Latitude: 51.5755 / 51°34'31"N

Longitude: -2.8008 / 2°48'2"W

OS Eastings: 344600

OS Northings: 186593

OS Grid: ST446865

Mapcode National: GBR JG.CS7J

Mapcode Global: VH7BH.DNPL

Entry Name: Relict Seawall alongside Collister Pill Reen

Scheduled Date: 18 September 1995

Source: Cadw

Source ID: 1420

Cadw Legacy ID: MM226

Schedule Class: Maritime

Category: Seawall

Period: Medieval

County: Monmouthshire (Sir Fynwy)

Community: Magor with Undy (Magwyr gyda Gwndy)

Built-Up Area: Undy

Traditional County: Monmouthshire


The monument consists of a seawall running along the western side of Collister Pill Reen. This seawall was erected in the Middle Ages to enable the reclamation of the Gwent Levels in Undy parish and remained a sea defence until the enclosure of Caldicot Moor in 1850. The seawall is an earthen bank between 11m and 12m wide at the back and 5m wide on the top. It stands between 2m and 2.5m above the land to the west, but is almost level with the land on Caldicot Moor.

The monument is of national importance for its potential to enhance our knowledge of coastal defences. It retains significant archaeological potential, with a strong probability of the presence of associated archaeological features and deposits. The structure itself may be expected to contain archaeological information concerning chronology and building techniques. 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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