Roundhouse Farm was built around 1816 as a safe retreat for the local iron master Joseph Bailey. It has two storeys and 4ft. thick stone walls. There is a floor with iron joists and iron segment roof members overlaid in bricks and pitch. This is significant as one of the best surviving examples of the early use of structural cast-iron in Britain. The Round Towers are also two of the last private domestic structures built in Britain with a serious defensive purpose.

There is a low (5ft. high) Pennant sandstone wall running around a rectangular enclosure near the crest of the valleyside behind the ruin of the ironmasters' (Joseph & Crawshay Bailey's ?Nantyglo House; which also has the remains of a cast-iron ?verandah) house and overlooking the former site of the ironworks in the valley below.In the enclosure at the north is a fairly nondescript white-rendered farmhouse (which doesn't have an iron-framed roofs) and in the centre of the enclosure the long north-south range of the farm-buildings with eastward-pointing wings at its terminals. At the north-east and south-west terminals are the defensible towers that give the farm its distinctive name. The building of the towers is ascribed to 1816; their construction by the ironmasters apparently prompted by the Merthyr Riots of 1813. ?

There are two entrances for wheeled traffic through gaps in the north and south boundary walls adjacent to the corner towers. These have cast-iron plates for receiving the vertical hinge-rods of what were probably iron gates. A tramroad skirted the eastern side of the complex (now a rough road) and may have entered the complex from the north.All fittings for the towers were of cast-iron but those from the south-west tower have been almost entirely removed and those from the north-east have been damaged to a small degree by the removal of much of the cast-iron for scrap in 1942-45.

The south-west tower was originally one storey higher than the north-eastern one and housed four families. It had been lived-in to the 1930s. Masonry partition walls are visible in the basement and the ground-floor is substantially intact. The first-floor has substantially-ruined walls and the top second-floor is completely missing. The stone spiral staircase (that both towers have) with slabs corbelled-out from the interior walls is still mostly intact. The cast-iron floor-joists have been cut-off at the point where they entered the stone external walls. Other cast-iron fittings remain: the cast-iron window-frames; the multiple cast-iron lintels over the deeply-splayed window slits and the external cast-iron sill-plates.

The north-east tower has been restored but a main cast-iron beam holding the iron roof has recently sheared and is at present supported on an infill of scaffolding. Lattices of main and subsidiary cast-iron beam supports for the (missing) floors remain with smaller beams fitting into sockets on the larger. The roof is of wedge-shapes cast-iron plates getting successively smaller until the innermost rings of plates slope down to a circular cast-iron plate at the centre. The outer-plates of the roof rest on a composite cast-iron ring-beam laid in segments on the inner wall-capping and segments of a similarly-sectioned beam are positioned on the inner-side of the deeply-splayed windows. There is a small parapet wall around the roof.

The iron door to the building has two musket-holes in its lower part with iron swivelling-covers on their inside faces. An iron perforated-plate set in the ground to the right of the door covers the loading-shoot into the tower basement. Part of a lathe and plaster partition remains on the first-floor of the tower which was also used as one or two workers dwellings (a secondary use?). The long-range has a toothed-joint two-thirds of the way from its northern end that indicates that the building was constructed in two phases. All joists for the first-floor and ceiling are in cast-iron as are the roof-trusses with their curved roof-ties. Cast-iron door-frames remain but any iron doors have gone.

RCAHMW, 25 April 2003.