A great landmark in the industrial development of the area was the opening of the Rhymney Railroad to Cardiff in 1858. This made possible a great expansion in the coal industry. The project was planned in the autumn of 1853 and the first sod was turned near Bargoed, in November of that year. The northern portion of the line was opened for goods traffic on 28th December 1857 and for passengers on 31 March 1858.
A train carrying a number of heavily laden trucks of iron left Rhymney where an immense crowd of people had assembled to see it start. On its way to Hengoed the inhabitants flocked to greet the train on its historic run. As the southern portion of the line to Cardiff had not been completed, it then went across the Hengoed Viaduct to Pontypool and thence to Newport. This Viaduct, which has been so prominent a landmark in the Rhymney Valley, was completed on 4th November, 1857.
On 25th February, 1858, the southern portion of the line was completed and opened for goods traffic. It was opened for passenger services on 31 March 1858. The extention from Caerphilly where it branched west to Nantgarw through a deep cutting and on to join the Taff Vale Railway at Taffs Well, thence it ran to the Bute East Dock at Cardiff, did not open until 1 April 1871.
On that opening day two trains, one carrying iron and the other coal, passed down the entire length of the line from Rhymney to the terminus then situated at the Bute East Dock. These trains were gaily decked with a profusion of flags and evergreens and their appearance in Cardiff caused quite a commotion in those streets adjoining the railway. Passengers were carried for the first time on 31 March 1858. There were two trains a day and the return fares to Cardiff were : Hengoed l/3d.; Pengam l/5d.; Bargoed l/6d.; Tirphil l/9d.; and Rhymney 2/-.
The journey from Cardiff to Bargoed took one hour ten minutes, which was a reasonably good time especially when we consider that the train waited at Hengoed for ten minutes to allow for changes to the Viaduct line.
Easy contact with Cardiff was now possible and one effect was that more Rhymney Valley news appeared in the " Cardiff and Merthyr Guardian ". One writer urged that now they had the dignity of a railway, the place popularly called " Gomorrah " should be known as Pontlottyn. Indeed other villages actually changed their names with the coming of the railway, for instance Charlestown became Bargoed and George Inn became Brithdir.
Ladies' fashions were hardly suitable for train travel in those days, because in 1859 there appeared in the press, under the heading of " Distressing Incident", a paragraph which recorded how a young lady failed to get into a compartment on the train at Bargoed on account of the fact that she was wearing a voluminous crinoline. The train went on to Cardiff leaving the stranded blushing passenger on the platform.
In 1876 the joint GWR/RR line from Llancaiach (Nelson) to Cae Harris Station was completed and was opened for goods traffic on 3 January 1876 anf passengers on 1 February 1876. This line included a one and a half mile branch from Cwm Bargoed station to Fochriw Colliery which was laid by the Dowlais Iron Company.