1786 In his will, Anthony left Thomas Bacon (his son by his mistress) the Plymouth furnace.
Needing transport facilities and because the owners of the Cyfarthfa Ironworks dominated the management of the Glamorganshire Canal, the other ironworks, including Plymouth, built the Merthyr Tramroad to bypass the upper sections of the canal.
1800 The railway, also known as The Plymouth, or Hill's Tramway, was constructed without Act of Parliament but using the powers of Glamorganshire Canal Co's Act - 36 Geo. III., c. 69 - to carry coal from the Plymouth colliery and iron from the Penydarran and Dowlais works in the vicinity of Merthyr to the Aberdare Canal at a point near (what became) the Abercynon Station of the Taff Vale Railway - formerly known as Aberdare Junction Station - a distance of 9 miles parallel with the canal. It opened in 1800 and remained in use until 1875; the rails were taken up in 1890. When the World's Columbian Exhibition was held in Chicago in 1893, the Plymouth Company sent ten of the rails and two of the original wagons to it - see figure above
1803 As soon as he came of age Thomas Bacon sold the works to Richard Hill.
Richard Hill and his son were anxious to improve their business by adding a forge and mills but were very short of capital for such an extension. They obtained an injection of capital from A. Struttle and from Hill's son-in-law, John Nathaniel Miers, to form the Plymouth Forge Company.
1806 Richard Hill died
By 1813 Struttle and Miers had left the business; the three Hill brothers (Richard II, John and Anthony) became partners. They enlarged Plymouth.
In 1815 a fourth furnace was built at Plymouth.
The Plymouth Works relied on water power, long after its use had ended elsewhere. In order to re-use the water, the works expanded by adding 2 other, separate units: the Pentrebach Forge and Dyffryn Furnaces.
1819 Erected the first furnace at Dyffryn
c.1824 two additional furnaces and a steam-blowing engine were projected and another water-wheel put up at Pentrebach, called afterwards the Little Mill. When the 8th furnace was built, Mr. Mushet described it as the largest in the world.
1824 Plymouth was producing 12,000 tons per annum
1835 Richard's son, Anthony, by then owner of the Plymouth Ironworks, asked Isambard Kingdom Brunel, to estimate the cost of building a railway from Merthyr to Cardiff and to Bute Docks, which became the Taff Vale Railway.
Steam power was finally introduced following the dry summers of 1843 and 1844. This led to a dramatic increase in output.
1862 Richard Fothergill, owner of the Aberdare Ironworks, acquired the whole of the Plymouth Ironworks on the death of Anthony Hill; he converted them from the cold blast system to the hot blast so that these works were serious competition for the great concerns at Dowlais and Cyfarthfa.
1875 As a result of the introduction of the Bessemer process, and owing to coal strikes, Fothergill's companies failed, as did many others.
Plymouth Forge Co
1803 Plymouth Forge Company was set up.
1807 When a third furnace was erected at Plymouth, a company was formed under the name of Plymouth Forge Co composed of Mr. R. Hill, senior, Mr. R. Hill, junior, Mr. Myers, and Mr. Strattel. They erected the Pentrebach Works, with the aim of making up to 100 tons a week of bar iron.
While the site of the Plymouth Works, the earliest works, lay to the northeast of the area, the Pentrebach Forge and Dyffryn furnaces were located on the west side of theRiver Taff. The remains of the ironworks were the subject of two large reclamation schemes undertaken during 1974.
The Plymouth Forge Co established a a forge at Pentrebach in 1807, followed by a rolling mill in 1841.
The forge was connected with Plymouth Ironworks to the north and Dyffrin furnaces to the south by the Merthyr Tramroad.
By 1919 the sites of the former ironworks had been put to alternative uses: a brickworks occupied the site of the Pentrebach Ironworks.
1819 The Hills erected the first furnace at Dyffryn
1824 Two new furnaces were erected at the Dyffryn Ironworks by Anthony Hill.
1861 A plan drawn in 1861 shows five blast furnaces, numbered 5, 6, 7, 8 & 10, kilns and limestone sheds, a refinery, cast house, engine houses, a double waterwheel, and a fitting-up shop.
Some time after the furnaces went out of use, the Plymouth Company sank a coal pit on the site. All surface remains were swept away in the late 1970s..
By 1919 the Dyffryn Furnaces had become the Dyffryn Boiler Works
This channel supplied water to the waterwheels at the succession of works (Plymouth, Pentrebach, Dyffryn). The water was taken from the Glamorganshire Canal at a point adjacent to Ynysfach Ironworks. The feeder was on the opposite side of the River Taff from the canal, requiring the water to be taken under the river at the Plymouth Weir by a syphon. Having done its work at Dyffryn furnaces, the water entered the River Taff, from where the Pontyrhun Pump lifted water back into the Glamorganshire Canal.
From the Merthyr Telegraph, and General Advertiser for the Iron Districts of South Wales, 10 September 1870.
'THE PLYMOUTH IRON WORKS.
'At 1.30 p.m. on Tuesday a special train conveyed the members of the Institute and the visitors, about 200 in number, from the station of the Great Western Railway over the private railway of the Plymouth Company to the Plymouth Works. The party, led by Mr Fothergill and the president of the Institute, the Duke of Devonshire, went over the blast furnaces, examined the Pentrebach finishing establishment, and witnessed the results of the labour and skill of the owners and staff of the Plymouth Company. A short sketch of the works will enable the readers to realise what the visitors saw. These works are situated south of Merthyr, and are to be seen on the right-hand side whilst travelling by rail from Troedyrhiw to Merthyr. They were purchased seven years ago of the executors of the late Mr Anthony Hill by Messrs. Richard Fothergill, M.P., and T. A. Hankey, the present owners. They consist of four separate works, namely, Plymouth, Pentrebach, and Duffryn, for Penydarran may now be considered part of the Plymouth works. These works, taken together, are very considerable, and give employment to a large number of hands.
'Plymouth consists of five cold blast furnaces, three only of which are now at work, with one 90-inch horizontal blowing engine, and two water-wheels driving four 66-inch cylinders. The iron used in the manufacture of the Great Eastern S.S. cable that stood the great storm of Holyhead was made at these works.
'Pentrebach is situated about a mile below Plymouth, at a sufficiently lower level for the diameter of the water-wheels which assist in driving the extensive forges and mills. This is the manufacturing division of the works, and consists of four forges, with the necessary trains and steam-hammers, two rail mills, two No. 2 mills, and a small bar-iron mill. Two small bar mills and a slitting mill are now idle, the whole force of the establishment being directed to the manufacture of rails. These works are conducted with great energy and skill, Mr Fothergill taking an active part in the management, assisted by his able and indefatigable engineer, Mr Hosgood. We were told that the mills now at work rolled upwards of 1,000 tons of manufactured iron in the course of last week. They are capable of rolling bars from six inches square, of ordinary lengths, down to slitting and 3-16 inch guide-iron
'Duffryn [Dyffryn] consists of five blast furnaces, four of which are now at three[?] on cold and one on hot blast. There are two blowing engines, with cylinders with 90 and 122 inches in diameter, and four 66-inch cylinder driven by two water-wheels, with refineries and coke ovens. The coke chiefly used at the blast furnaces is the open air coke, made from the best steam coal, which is very free from sulphur.
'Penydarran works, situated just above the town, were formerly owned and managed by the late Mr Foreman. They were at one time very extensive works, but of late years have been quite idle, the great furnaces and sheds silent, gloomy, and deserted. They are now the freehold property of the Plymouth Iron Company, and getting into work again. One of these forges started a few weeks ago, and a second is nearly ready. These works consist of seven blast furnaces, four refineries, two large blast engines with blowing cylinders, 104 and 122 inches respectively, and two forges with the necessary furnaces. The blasting engines are now being thoroughly repaired, one of which with four refineries, will start in a few days, whilst the other, with two blast furnaces, is being proceeded with.
'There are a number of locomotive engines used about these works, several of which are 20ft. 8in. [!] gauge, which, very materially lessen the cost of transmitting the raw material and manufactured iron from one place to another.
'PLYMOUTH COLLIERIES. In connection with the ironworks are six collieries yielding on an average 1,500 tons per day. There are at the South Dyffryn pits an immense pumping engine and a pair of gigantic moving engines of Cornish manufacture. These, for want of time, the visitors were unable to see on Tuesday. The collieries are under the management of Mr John Smith, one of the ablest, most successful, and least pretending of the many able mineral engineers of the district. Mr Smith is also manager of the extensive collieries of the Aberdare Iron Company in the Aberdare Valley.'
'CAPTAINS OF INDUSTRY.
To the Editor of the 'Western Mail'
Sir, - Will you please allow me to correct some inaccuracies which are contained in 'the memoir of Mr. William Thomas Lewis by Major Evan R. Jones, and reproduced in your issue of last Saturday? Mr. William Thomas Lewis's father was the mechanic or millwright (not the engineer) of the Plymouth Ironworks during the time tbey were owned by Mr. Hill. He resided at Pentrebach, the forges and mills of the Plymouth Works being close by. One mile north stood the Plymouth and one mile south the Dyffryn Blast Furnaces, hence the subject of the memoir had not occasion to walk nearly the two miles. Mr. Hill would not allow of anyone being apprenticed, and, therefore, to say that Mr. William Thomas Lewis was must be inaccurate. The description of working is equally so; and, as regards what appears the culminating point- viz., becoming his father's assistant, permit me to state the present High Sheriff of Breconshire asked me, asa favour; to allow his leaving my office to go to Mr. Clark. In the reference to Brunel is another error. All drawings for rails passed through my hands, if not actually made by myself.
Mr. Hill was justly proud of the excellence of his rails. He made a somewhat severe course of experiments, had careful observations taken of each, and eventually obtained such a price for his iron rails as none other ever had. Not only were drawings made of the rails, but of the grooves, and in some cases the position and amount of every bar forming the pile had to be delineated on the finished rail. Possibly this had some influence; but, whether in that or any other department, there was always an earnest endeavour to teach the draughtsmen under me. I may add that Mr. Henry Watkin Lewis was, subsequent to his brother leaving, in my office for a while. Amongst others who also were in my office were Mr. A. G Kyle, who, ever since leaving Plymouth, has been enineer of Messrs. Hutchinson's Cemical Works at Widnes; and Mr. Jacob Rees, engineer of the Ocean Collieries and School Board architect. Mr. Morgan Thomas, the engineer of the Bargoed Coal Company at Deri, can also corroborate the accuracy of most of my statements. It is with some diffidence this is sent for publication; but, as the statement in your issue is in somue things unfair to myself, I appeal to your sense of justice to allow the insertion of this at an early opporturnity.- I am, &c., T. CRISWICK, Swansea, Aug. 4.'
Sources of Information
- The Engineer 1924/07/11
- Historic Landscape Characterisation of Merthyr Tydfil
- The history of the iron, steel, tinplate and ... other trades of Wales (1903) by Charles Wilkins 
- The Times, 23 October 1824
- The Times, Jun 01, 1875
- The history of the iron, steel, tinplate and ... other trades of Wales (1903) by Charles Wilkins 
- Wikipedia 
- 'Mines, Mills and Furnaces' by D. Morgan Rees, National Museum of Wales/HMSO, 1969
- 'The Glamorganshire and Aberdare Canals' Vol. 1, by Stephen Rowson and Ian L. Wright, Black Dwarf Publications, 2001, p.96
- 'The Glamorganshire and Aberdare Canals' Vol. 2, by Stephen Rowson and Ian L. Wright, Black Dwarf Publications, 2001
- Western Mail, 6 August 1884