Christie commenced construction of the tramroad in about 1821. The earliest section constructed was that between the limestone quarries at Pwll Byfre and Castell-du Farm at
Sennybridge. The model farm of Cnewr was constructed at the halfway point of this stretch of tramroad. A second stage was to build a tramroad to serve the Drim Colliery near
Onllwyn which Christie had leased in 1822. From the colliery the line ran northeastwards to the village of
Coelbren and then across the
Nant Llech just above
Henrhyd Falls and around the flanks of the hill north to Penwyllt. Initially Christie's probable intention was to link this line to that at Pwll Byfre by an incline through what is now the
Ogof Ffynnon Ddu National Nature Reserve. This scheme was abandoned and instead the line from the Drim was taken northwards along the contours of the eastern side of the valley past the quarries at Penwyllt, wrapping around the western slopes of
Fan Gyhirych and over the pass at Bwlch Bryn-rhudd then northeastwards to join the original line just south of the
Nant Gyhirych stream. Christie further extended the tramroad southwestwards from its southern terminus to a colliery at Gwaun Clawdd on the northern slopes of Mynydd y Drum and connected it to the
Swansea Canal at Cae'r Lan near
Abercraf. During the 1820s he was a major shipper of coal on the canal which was shipped through Swansea. Christie was declared bankrupt in December 1827 and the Great Forest, including the tramroad and most of his other assets, passed to his principal creditor, Joseph Claypon, of the banking house of Garfit & Claypon in
Boston, Lincolnshire. Claypon built a further extension southwest and then west from the Drim colliery to join the Swansea Canal and to supply limestone to the
Ynyscedwyn Ironworks at
Ystradgynlais. Following the death of Claypon in 1859 much of Christie's original route was ultimately sold to the railway contractor,
John Dickson and incorporated by him into the
Neath and Brecon Railway. Claypon's Tramroad was largely unaffected by this, although sections at Ystradgynlais were converted into colliery railways or taken over by the
Swansea Vale Railway. == Main present-day route ==