5th October 1839 saw the opening of West Bute Dock in Cardiff, which resulted in Cardiff becoming one of the biggest coal exporting docks in the world by 1913.
Following the discovery and development of coal found in the Cynon and Rhondda valleys and the rapid expansion of Merthyr's iron operations in the wake of the Industrial revolution, their export required a sea connection to the Bristol Channel.
The Glamorganshire Canal was opened in 1794, linking Cardiff with Merthyr and by the 1830s Cardiff was shipping almost half of Britain's iron exports, which led in 1839 to John Crichton-Stuart, 2nd Marquess of Bute and Cardiff's foremost landowner, being instrumental in the construction of the (West) Bute Dock, which was opened on 5th October 1839.
Two years later, the Taff Vale Railway was opened and with the construction of the new East Bute Dock from 1855, coal supplanted iron as the industrial foundation of South Wales, with coal exports increasing from 44,350 to 2.219 million tonnes, between 1840 and 1870.
However, frustration at the lack of further development at Cardiff led to rival docks being opened in 1865 at Penarth and in 1889 at Barry. These developments eventually resulted in the opening of the Roath Dock in 1887 and the Queen Alexandra Dock in 1907, which saw coal exports from the South Wales Coalfield via Cardiff rise to 10,700,000 tons by 1913, making Cardiff the biggest coal exporting dock in the world.