Ancient Monuments

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Garnddyrys Ironworks (Site of) and adjacent Tramway

A Scheduled Monument in Llanfoist Fawr (Llan-ffwyst Fawr), Monmouthshire (Sir Fynwy)

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Latitude: 51.8 / 51°47'59"N

Longitude: -3.0784 / 3°4'42"W

OS Eastings: 325733

OS Northings: 211807

OS Grid: SO257118

Mapcode National: GBR F3.XT6K

Mapcode Global: VH79C.L0FZ

Entry Name: Garnddyrys Ironworks (Site of) and adjacent Tramway

Scheduled Date: 4 July 1977

Source: Cadw

Source ID: 2413

Cadw Legacy ID: MM189

Schedule Class: Industrial

Category: Industrial monument

Period: Post Medieval/Modern

County: Monmouthshire (Sir Fynwy)

Community: Llanfoist Fawr (Llan-ffwyst Fawr)

Traditional County: Monmouthshire


The monument consists of the remains of an iron forge and section of tramroad located at 1300ft AOD on the NW side of the Blorenge mountain. The forge forms part of the complex of industrial sites associated with the Blaenavon Ironworks, and is where pig iron from the furnaces in Blaenavon was converted into wrought iron bars or rails. At its peak, the forge employed 450 people and produced 200 tons of wrought iron per week.

The forge at Garnddyrys was built in 1817 by the Blaenavon company and consisted of a complex of steam powered furnaces, puddling furnaces and rolling mills together with a weighing house and houses for the workers. Pig iron was brought from the ironworks in Blaenavon along Hill’s Tramroad, a primitive railway built by Thomas Hill in the years after 1815. The tramroad passed through the Pwll Du Tunnel to Garnddyrys and then around the Blorenge to Llanfoist. The construction of the section of tramroad to the S of the forge complex, included in the scheduled area, involved cutting a terrace into the steep hillside and building a substantial retaining wall. In places the sleeper stones that would have held the rails in place can still be seen through the turf. There are the remains of a stone building adjacent to the tramline to the S of the forge and this is thought to have been a blacksmiths shop. The tramroad continues N through Garnddyrys, entering a cut and cover tunnel at the N end of the lower pond. This extends for around 150m and was built to prevent the tramroad from being buried beneath piles of slag from the forge.

On the forge site are the remains of two large ponds, the N of which (upper pond) would have supplied water to the steam engines that powered the furnaces. Water would have been fed into the upper pond from the slopes of the Blorenge above. Records reveal that there were two steam engines on the site, providing blast for the furnaces. The arched outlet through which water was fed to the steam engines can be seen towards the top of the retaining wall on the W side of the upper pond. Below the retaining wall are the foundations of the forge buildings, including a structure called the Manager’s house that was excavated in the 1970s – this large building had a cellar and two fireplaces but given its proximity to the forge is unlikely to have had a domestic function. At the N end of the site, immediately N of the furnaces, are the foundations of workers cottages. These form three sides of a square, with the N and S sides more easily discernable.

On the W side of the site is a large and distinctive heap of slag, and the W slopes below the forge are littered with boulders of slag up to several metres across.

The site ceased production in the 1860s, and was replaced by the new forge at Forgeside. It had become uneconomic to transport pig iron to this remote forge site after the railway came to Blaenavon and replaced the canal as the main means of transport in the 1850s.

The monument is of national importance for its potential to enhance our knowledge of 19th century iron working and other industrial practices. 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.

Source: Cadw

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