The Aeolus Waterwheel – Merthyr’s Great Wonder

When Rev Sir Thomas Cullum (8th Baronet Cullum) visited Merthyr Tydfil in 1811, one of the sights he was most taken with was the mighty Aeolus Waterwheel at the Cyfarthfa Ironworks, and he even called it ‘the wonder of the place’. Some contemporary accounts actually refer to it as ‘the Eighth Wonder of the World‘. I wonder how many people in Merthyr have actually heard of it nowadays?

‘Cyfarthfa Works and Waterwheel’ by William Pamplin. The Aeolus Waterwheel can clearly be seen at the centre of the illustration. Photo courtesy of Cyfarthfa Castle Museum & Art Gallery

When Richard Crawshay became sole owner of the Cyfarthfa Works in 1791, he began making plans to extend the works and come up with innovative ways to increase iron production. In 1792, he made the engineer Watkin George a partner in the firm, and the latter began making significant progress in maximising the potential of the works.

His major contribution was the construction between 1793 and 1797 of a huge overshot waterwheel to provide the air for the four blast furnaces.

According to volume 5 of Rees’s Manufacturing Industry (1819-20):

“…..the water-wheel is 50 feet in diameter and six feet wide: it is chiefly made of cast iron, and has 156 buckets. The axle is a hollow tube, and is strengthened by twenty-four pieces of timber applied around it. On each end of the axis is a cog-wheel of twenty-three feet diameter, which turns a pinion. On the axis of these are two cranks, and fly-wheel twenty-two feet diameter, and twelve tons weight; each of the cranks gives motion to a lever, like that of a large steam-engine, and works the piston of a blowing cylinder or air-pump 52½ inches in diameter, and five feet stroke, which blows air into the furnace, both when the piston goes up and down. The work on the other side being the same, it actuates in the whole four of these double cylinders; the wheel makes about two and a half turns per minute, and each cylinder makes ten strokes.”

At the time, it was the largest waterwheel of its kind in the world and was named Aeolus after a character in Greek Mythology. Aeolus, as mentioned in the Odyssey and the Aeneid,  was the keeper of the winds and king of the island of Aeolia, one of the abrupt rocky Lipara islands close to Sicily. Later classical writers regarded him as a god.

The wheel was operated by water fed from streams across the river and transported by a massive iron and wood double aqueduct mounted on stone piers between 60 and 70 feet high. This was the famous Gwynne Aqueduct. Sir Charles Manby (later Secretary of the Institution of Civil Engineers) visited Merthyr and commented that the aqueduct:

“…..maintained an apparent lightness of the whole that contrasted with the massy [sic] boundary of the river, has not only a singular, but also a very interesting and pleasing appearance.”

Gwynne Aqueduct from a painting by Penry Williams

This is the same aqueduct that was mentioned in the previous post about the Pont-y-cafnau (

The Aeolus Waterwheel continued to power the blast furnaces until the 1820’s when it was replaced by a steam powered engine, and was subsequently demolished.

Merthyr’s Bridges: Pont-y-Cafnau

The Grade II* listed Pont-y-Cafnau over the River Taff in Cyfarthfa is thought to be the world’s oldest iron tramroad bridge. An influential early prototype and is a unique survivor of its kind, it is also an aqueduct, with a water trough below the deck. Its designer was Watkin George (c.1759-1822), the chief engineer of the nearby Cyfarthfa Ironworks, which it served, and the bridge/aqueduct enabled the movement of limestone on its tram rails and a water supply, both for the ironworks. The limestone came from the Gurnos Quarries, and the water from a leat supplied by the Taf Fechan. The water was used to drive waterwheels to generate power to run machinery for iron smelting.

The structure was designed sometime in 1792 and construction began in January 1793 and the bridge was completed some time before 1796.

The distinctive appearance of the bridge is created by two large cast iron A-frames, which span the river, their raking ends embedded in the coursed rubble abutment walls on either side. The span measures 14.3m. Three transverse iron beams, at the halfway and quarter-points, connect the A-frames and support the deck. George was originally a carpenter and he used carpentry techniques for the ironwork – mortise-and-tenon and dovetail joints can be seen.

The deck consists of rectangular aqueduct trough, 1.9m wide and 610mm high, made of long iron plates. The trough is covered by an iron deck, cast in sections, on which was laid the 1.22m (4ft) gauge tramroad. Wagons ran on straight iron rails carried on iron chairs. Some chairs and sleepers are still in place along the full length and segments of rail survive at the southern end.

The cast iron handrails were supported at the centre and quarter points of the span. Most of the original cast iron railings have now been replaced.

In 1795, a second bridge was cast from the same patterns to carry an extension of the tramroad and aqueduct from the ironworks to the Glamorganshire Canal. This bridge, sadly, no longer exists.

Shortly after Pont-y-Cafnau was completed, the Gwynne Water Aqueduct (completed 1796) was constructed over the top of it. Gwynne Water was 185m long, built entirely of timber and used the cast iron uprights of the bridge for support. it supplied water to the 15m diameter Aeolus waterwheel, also designed by George, which powered an air pump for the blast furnaces. Presumably, the extra bracing that has been added to the bridge dates from this work. Nothing of the second aqueduct remains.

Pont-y-Cafnau is a Scheduled Ancient Monument as well as a Grade II* listed structure. The iron trough no longer carries water. However, its name means “bridge of troughs”, testifying to its former life.

The bridge influenced the construction of other, better known, aqueducts. In 1794, Shropshire ironmaster William Reynolds (1758-1803) made a sketch of it. Reynolds’ involvement in the rebuilding of Thomas Telford’s (1757-1834) navigable Longdon on Tern Aqueduct on the Shrewsbury Canal in 1796 seems to have led Telford to reconsider using stone and to opt instead for cast iron. It was also the prototype for Telford’s famous Pontcysyllte Aqueduct, which opened in 1805.

Pont-y-Cafnau in March 2017