at SO 233137 and SO 255176, the latter being the Llam-march Tramroad and Aqueduct Bridge of 1811 which also carried water from the Clydach to the Clydach Ironworks Rolling Mill via a leat. Govilon Tramroad Engineered by Crawshay Bailey in 1821, this tramroad (sometimes also referred to as Bailey's Tramroad) traverses the southeastern slopes of the gorge below and parallel to the Llam-march Tramroad. It connected the Bailey's ironworks at Nantyglo with the Monmouthshire and Brecon Canal at Govilon, in the Usk Valley. Merthyr Tredegar and Abergavenny Railway See main article on Merthyr, Tredegar and Abergavenny Railway The railway was constructed in 1862 as a single line, following in part, the line of an earlier tramroad. Four years later it became a part of the London and North Western Railway network and in 1877 the line was doubled along its entire length. The routing of the line through the gorge was a considerable engineering challenge requiring the digging of several tunnels and the construction of an impressive curving viaduct across the ravine of the Nant Dyar. The line continued in operation until the 1950s when British Rail decided to close it as being uneconomical to run. The last trains ran along it in June 1958. The larger part of the track-bed has now been converted to a cycleway, forming part of route 46 of the National Cycle Network. Roads Merthyr Tydfil to Govilon Turnpike The Merthyr Tydfil to Govilon Turnpike was authorised by Act of Parliament and laid through the valley in 1812–13. This formed the main road through the gorge until the modern road was built. Heads of the Valleys Road See main article on A465 road The A465 was dualled through the gorge between 2013 and 2021. The previous alignment of this major trunk road through the gorge was constructed in the 1960s by John Morgan (Construction) Ltd of Cardiff. Achieving a consistent gradient of 1 in 20 for a distance of it climbs from Gilwern to Brynmawr. Its construction involved considerable cutting and embanking and some sections were built out over the gorge on concrete pillars. Work began in March 1960 and it was opened to traffic in 1962. It was a single-carriageway route with two west-bound lanes running up the gorge. Work to construct a dual carriageway through the gorge began in January 2015. Environmental protection The entire Clydach Gorge falls within the Brecon Beacons National