The Rhymney Railway was virtually a single stretch of main line, some fifty miles in length, by which the Rhymney Valley was connected to the docks at Cardiff in the county of Glamorgan, South Wales.
The aim of the railway was to gain access to the large iron works and collieries at the extreme north of the Valley. Short extensions, connecting with other railways, gave the Rhymney routes to take its (largely mineral) traffic to the Midlands and the North of England, or opened up connections to collieries and iron works. Some of those routes were worked jointly with other companies, particularly the London and North Western Railway (LNWR).
Growth of the railway
The original incorporation was in 1854, and the railway was opened in various sections as follows:
- Rhymney to Hengoed, January 1858
- Hengoed - Walnut Tree Junction, February 1858
- line into Cardiff 1864
- Rhymney - Nantybwch, giving access to the LNWR. This section was worked jointly by the two companies April 1871
- Ystrad Mynach - Penallta Junction, giving access to the Great Western Railway and the Aberdare Valley, April 1871
- Taff Bargoed branch giving access to the Dowlais Iron Works. Nine miles in length, with a gradient of 1:40, it had heavy usage. In 1911 the Rhymney conveyed over 300,000 tons of iron and iron ore per annum over this route. Opened 1 January 1876
- Quaker's Yard - Cyfarthfa, authorised 1882
- Aber branch, 1890
- Ystrad Mynach - Cylla Valley, 1895
The Rhymney owned 120 locomotives in 1911. By then the total mileage of the Rhymney was over 61 miles; a further 16 miles of 'foreign' track was also worked over. Over two million tons of freight had been carried.
- Details above taken from The Railway Year Book 1912 (The Railway Publishing Company Ltd)
Although the Rhymney was nominally independent until absorption in the Great Western Railway on 1 January 1922, the same managing director, in 1917, took over control of the line and the Taff Vale Railway and the Cardiff Railway, making them to all and intents and purposes one undertaking.
The stations of the line from Cardiff to Rhymney were as follows:-
- Cardiff Parade
- Heath High Level
- Cefn On Halt (now replaced by nearby Lisvane and Thornhill railway station)
- here is the Caerphilly tunnel 1.1 miles (1.77 km) in length
- Ystrad Mynach
- Gilfach Fargoed
- Tirphil (New Tredegar)
- Rhymney Bridge (joint station with LNWR)
- Nantybwch (also joint station with LNWR)
From south to north these were:
- Caerphilly - Taffs Well connecting with the Taff Vale Railway Openeed 1858
- Senghenydd branch: with intermediate stations serving:
- From Ystrad Mynach a spur connected with the GWR; from Treharris on that line there was a Rhymney Railway line direct to Merthyr Tydfil over the Taff-Bargoed Joint Line undertaking
- Deri branch connecting at Deri Junction with the Brecon and Merthyr Railway
All of those branches have since been closed.
Cornelius Lundie, from the outset of the line and for more than 40 years, was General Manager, Traffic Manager and Superintendent of the line. Upon his retirement in 1904, the Rhymney did a spring cleaning, which notably included the scrapping of his favourite engine, which he had been preserving for a number of years.
- Thomas Clements (1858–1862)
- Matthew Mordue (1862–1863)
- John Kendall (1863–1869)
- John Canty (1869–1884)
- Richard Jenkins (1884–1906)
- C. T. Hurry Riches (1906–1922)
C. T. Hurry Riches was the son of Tom Hurry Riches, Locomotive Superintendent of the Taff Vale Railway (1873–1910). Kendall had an unfortunately short career with the Rhymney, which was cut short when he visited the Brecon and Merthyr Railway to examine a new engine of theirs on 10 June 1869. It overturned at Maesycwmmer, killing him and his B&MR counterpart, J.T. Simpson.
The early locomotives were tender engines, whether for passenger or goods:
- 0-6-0 Vulcan Foundry 1857: inside frames; freight
- 2-4-0 Vulcan Foundry 1858, 1861: passenger locomotives
- 0-6-0 Kitson 1859-1868: double frames, outside cranks; freight
- 0-6-0 ST 1872 onwards: various builders. All Rhymney locomotives from then were of this type.
- Notes taken from The Railway Magazine February 1923
- Rhymney Railway A class 0-6-2T
- Rhymney Railway B class 0-6-0WT
- Rhymney Railway I class 0-6-0ST
- Rhymney Railway K class 0-6-2ST
- Rhymney Railway L class 2-4-2ST
- Rhymney Railway L1 class 0-6-2ST
- Rhymney Railway M class 0-6-2T
- Rhymney Railway P class 0-6-2T
- Rhymney Railway R class 0-6-2T
- Rhymney Railway S class 0-6-0T
- Rhymney Railway S1 class 0-6-0T
The "main" line is now largely in use as the Rhymney Line. Evening trains traditionally stop closer and closer to Cardiff as the night wears on. For example, the last trains typically only go as far as Ystrad Mynach station.
Several original Rhymney Railway coaches have survived into the present day. Coaches No.95 and 109 stand in private residence. An unidentified six-wheel brake also resides in storage with the National Museums & Galleries of Wales.  Only one wagon, a goods van, is known to still exist today, stored at the National Museum of Wales. 
No locomotives still exist this day into preservation.
- pre-Grouping Atlas
- "Cornelius Lundie". steamindex.com. Retrieved 8 January 2009.
- "Tom Hurry Riches". steamindex.com. Retrieved 8 January 2009.
- Davies, F. K.; Firth, J. M.; Lucking, J. H.; Thomas, R. E.; Allcock, N. J.; Sterndale, A. C.; Barrie, D. S. M.; Reed, P. J. T.; Mountford, E. R. (April 1966). White, D. E., ed. The Locomotives of the Great Western Railway, part ten: Absorbed Engines, 1922–1947. RCTS. pp. K98, K196. ISBN 0-901115-20-7.
- The Rhymney Railway: including map, dates of opening
- Abandoned sections of the Rhymney Railway on cardiffrail