The area is most notable for being the site of a 1st-century Roman fort, and during the Industrial Revolution it housed Penydarren Ironworks the third largest of the great Merthyr works. Penydarren was also used by Richard Trevithick as the location for his experiments into steam locomotion. The community and ward has a population of 5,253, increasing to 5,419 at the 2011 Census.
Penydarren Park, the site of the Roman fort and the football ground, is today outside the community boundary.
Being located on a spur of land 700 feet (210 m) above sea level, just southwest of the River Taff, made Pen-y-Darren an ideal location to build an occupation outpost fort for the Romans in AD75, during the governorship of Sextus Julius Frontinus. It was during this period that he subdued the Silures and other hostile tribes of Wales by establishing a new base at Caerleon or Isca Augusta for Legio II Augusta, and this was one of a network of smaller forts fifteen to twenty kilometres apart for his auxiliary units.
The only information known about the fort is from the later excavations undertaken during the construction of the football stadium in 1905 by Frank Treharne-James, and in 1957 during the demolition of Penydarren House.
From the combination of these works, it is presently estimated that the fort had a turf and clay rampart 8.2 metres (27 ft) wide, set on a cobble foundation and separated by a narrow berm of 0.6 metres (2 ft 0 in) wide from its double ditch. The inner ditch was 0.4 metres (1 ft 4 in) wide, the outer 0.3 metres (1 ft 0 in) wide, separated by a berm of 2.5 metres (8 ft 2 in). If a well recorded by Treharne-James in 1905 was centrally placed within the principia, and a square outline is assumed, then the fort had dimensions of 152 metres (499 ft) across the rampart crests, covering an area of 2.3 hectares (5.7 acres).
Flavian pottery confirms the origin of the fort as a wooden structure, replaced in stone around AD 100, with the bath house located outside the fort's southern defences contemporary with the rebuilding. The latest pottery recovered is Trajanic, confirming that the site was abandoned in the Hadrianic period, with its garrison, moved to a new build fort at Gelligaer.
After Samuel Homfray came to South Wales, and establishing the Penydarren Ironworks, he won a bet with Richard Crawshay, and with the proceeds built Penydarren House in 1786 on the site of the Roman fort. It was during the construction that workmen first found Roman bricks and the remains of a tessellated pavement. Developed on a site opposite the works, but "sufficiently removed from the town by the extent of the pleasure grounds, and contains all the conveniences and the luxuries requisite for a family of wealth and importance," Homfray was waited on by servants who were dressed in a scarlet and buff livery, while he was driven everywhere in a coach and four horses.