The Glamorganshire canal, opened in 1794, runs from Cardiff to Merthyr Tydfil, with a branch to Aberdare.
In 1798 the first dock (12 acres in extent) was constructed at the terminus of the Glamorgan canal from Merthyr.
In Great Britain there is the South Welsh field, extending westward from the march of Monmouth shire to Kidwelly, and northward to Merthyr Tydfil.
The older part of the urban district is included in the parliamentary borough of Merthyr Tydfil, and also shares with Merthyr and Aberdare the services of a stipendiary magistrate.
There is only one line of railway, over which several companies, however, have running powers, so that the town may be reached by the Brecon & Merthyr railway from Merthyr, Cardiff and Newport, by the Cambrian from Builth Wells, or by the Midland from Hereford and Swansea respectively.