Knucklas (Welsh - Cnwclas) is a small village with a population of around 350 situated 2 miles north-west of Knighton in the upper valley of the River Teme; it is just south of the border with England. The Castle Mound is a protected ancient monument, the site of a castle believed to have been built by the Mortimers in the early C13th - a square stone fortification with four round towers on top of a steep hill. It was captured by a Welsh army in 1262 which destroyed the defences and attacked and destroyed by the forces of Owain Glyndwr in 1402 during his rebellion.
The spectacular Knucklas railway viaduct was constructed in 1865 and is Grade II listed. 23m high and 174m long, it is one of the most picturesque viaducts in Britain with 13 arches, a crenelated parapet with round towers at each end and square towers at the buttresses; it has featured in countless photographs by railway enthusiasts over the years.
Knucklas has a railway station on the Heart of Wales line which runs from Shrewsbury to Swansea.