High Quality Content by WIKIPEDIA articles! The Glamorganshire Canal was a canal in south Wales, UK, running from Merthyr Tydfil to Cardiff. Construction started in 1790, and the 25 miles (40 km) of canal was fully opened by 1794. Its primary purpose was to enable the Merthyr iron industries to transport their goods, and it later served the coal industry. It closed progressively between 1898 and 1951, as a result of subsidence and competition from the railways, and much of its course is now buried beneath the A470 Cardiff to Merthyr Tydfil trunk road.