ill-built croft at Nant-y-moch which was studied by Sir Cyril Fox58 or the somewhat earlier and more primitive house-sites excavated on Gelli- gaer Common.59 All those buildings, though earlier than the Elizabethan- Jacobean period, represent without much doubt the general level of peasant housing prior to the 'Great Rebuilding'.60 They will have been better houses than the wretched semi-underground dwellings which existed in Ireland in great numbers in the early nineteenth century, yet in general appearance they probably looked more like the Irish huts or cabins than Ffrwd Uchaf.61 Not until the second half of the seventeenth century were these primitive long-houses (or 'platform houses') rebuilt to the new standards. Unfortunately, the chronology of the change is imprecise. All we can say is that many of the old houses in the Faenor and Penderyn district seem to have been built (or rebuilt) in the second half of the seventeenth century, with some overlap into the early eighteenth century, and by the end of that period the process of improvement, and the raising of living standards which it implies, will have reached all the peasantry, or small farmers, whatever one chooses to call them. Within that social class some differentiation of wealth can be observed: Goetre and Garreg Fawr, Ystradfellte, suggest, by the number of their heated rooms, that they were very superior to, say, Cefn D'rysgoed. Thereafter, so far as our evidence goes, there was a slackening-off of building activity. It was the industrial revolution in South Wales which provided the next great impetus to improvement, beginning slowly in, perhaps, the 1820's, and then reaching a peak in the mid-century years. To this period more than any other the buildings owe their appearance. Many old farmhouses must have been heightened from one storey and attics to two storeys; re-roofing with blue slate instead of thatch was general, and in many houses there was a great increase in the number of rooms partly this was through heightening, so making more bedrooms, and partly through the addition of kitchens and parlours. Dairies were commonly added, often quite large ones; they are a direct reflection of the demand for milk and its products in the industrial towns. While it lasted the boom enabled land to be brought into use which can hardly have been used since the middle ages, but by the end of the First World War, and perhaps well before it,62 a decline had set in which has continued to our own day. 58 Sir Cyril Fox, 'A Croft in the Upper Nedd Valley, Ystradfellte, Brecknockshire', Antiquity, XIV, (1940), 363-376. 68 Arch. Camb., (1937), 247-268 ibid., (1939), 163-199. 80 See below. 81 C. O. Danachair, 'Semi-Underground Habitations' Galway Arcbaeol, and Hist. Soc., 75.80. 88 Cf. Fox's remarks on Nant-y-moch, as no. 58. There had been a decline in habitation of the high lands since it was built.