Ancient Monuments

History on the Ground

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Canal Aqueduct over the River Twrch, Ystalyfera

A Scheduled Monument in Ystradgynlais, Powys

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Latitude: 51.7683 / 51°46'6"N

Longitude: -3.7799 / 3°46'47"W

OS Eastings: 277278

OS Northings: 209239

OS Grid: SN772092

Mapcode National: GBR Y5.ZT6J

Mapcode Global: VH5G2.FTL8

Entry Name: Canal Aqueduct over the River Twrch, Ystalyfera

Scheduled Date: 8 November 1978

Source: Cadw

Source ID: 141

Cadw Legacy ID: GM396

Schedule Class: Water Supply and Drainage

Category: Aqueduct

Period: Post Medieval/Modern

County: Powys

Community: Ystradgynlais

Built-Up Area: Ystradgynlais

Traditional County: Glamorgan


The monument consists of the remains of an aqueduct, dating to the industrial period. This is the largest of the aqueducts which carried part of the original Swansea Canal, and it spans the Afon Twrch. The fast flowing nature of the river necessitated a weir to be built below the aqueduct to protect the piers and also to serve as a feeder. The total span of the aqueduct, which is built entirely of stone, is 21m.

The monument is of national importance for its potential to enhance our knowledge of industrial engineering and technology. 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, together with a strong probability of environmental evidence. Aqueducts may be part of a larger cluster of monuments 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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