The Norman conquest of South Wales started when William Fitzosbern, Earl of Hereford, crossed with an arny from Hereford into Gwent and established a castle-fort at Chepstow. Most of Glamorgan was later overrun by Robert Fitzhamon who built a castle at Cardiff on the site of the old Roman fort by 1091. The Normans thought their conquest of South Wales complete by the 12th century but continued to meet fierce resistance from local Welsh rulers. Resistance was strong in the mountains of the Darren Valley with a number of great battles fought in the area.
Construction of Caerphilly Castle began in in 1268 in 1268 in an attempt to cope with the threat from the hills to the north. Soon after, Llewellyn, Prince of Wales, came south in 1270 and razed Caerphilly Castle to the ground. However, the previous lord, de Clare regained possession and in 1282 the conquest of the whole of Wales by Edward the First, was recognised. Despite this the men from the hills of South Wales still refused to accept Norman rule with a rising in 1294-5 and another in 1314 led by Llewellyn Bren. Many battles took place on the Gelligaer mountain and Bren eventually surrendered to avoud further bloodshed. He was imprisoned in the Tower of London and his property was siezed. An amnesty was granted to the rebels but heavy fines were levied and it is believed that revenge exacted by the Normans caused evacuation of the hamlet which then existed at Dinas Niddfa and Clwyd Trawscae on the mountainside just above present day Deri.
The foundations of modern Wales were laid down in the 16th century. The Act of Union in 1536 made sweeping changes to the administrative system of South Wales. The political status of the Welsh people was changed from being primarily tenants of the local lord to that of subjects of the king. Henceforth there were no Welsh laws and Englisgh became the official language. Boundaries of Welsh counties were reorganised and the old lordship of Morganwg became the county of Glamorgan. The region of the Darran Valley became very much a pastoral backwater and the few small homesteads known at the time as Eglwys Gwladys took the name of Ysgwyddgwyn.
Ysgwyddgwyn remained scattered on the hillsides with little attempt to settle the floor of the valley as was done after industrialisation. The agricultural produce obtained from Ysgwyddgwyn was barely sufficient for local needs and there was little trade or contact with the outside world. The peasant population of the parish was considered to be of little importance and was largely left alone. Clergy were often absent and it was recorded at the time that there was “ignorance of Goddes Word, petty theft, idleness and extreme poverty” and that there were “neyther colledge nor free schools”.
Physically the Darran valley remained relatively untouched throughout the Middle Ages. The area was entirely rural for many years and the inhabitants made their living from the land. Most hamlets had their own masons, carpenters, tailors etc. and later came woollen mills. Most of the spinning and weaving of wool was done at home and then taken to the mills to be made into cloth and blankets. The local woollen industry survived into the middle of the 19th century but declined thereafter due to overwhelming competition from Yorkshire. What other industrial activity existed was confined to the corn mills. Grain in the area was ground into flour in local mills at Gelligaer, Gilfach Fargoed and Tiryfelin in Ysgwyddgwyn. Another famous mill was the old oat mill whose peculiarity was that its overflow went into the Darran river whilst the underflow entered the Rhymney river. This mill had an advanced roasting system which produced such a fine quality oatmeal that it became well known throughout Wales. It was demolished at the begining of the 20th century after being in existence for nearly 500 years. The Old Mill pub which now occupies the area is unlikely to match its longevity.
In general, the Darran Valley remained a pastoral backwater, little changed in methods of wage earning, and little altered in its physical appearance, until the industrial revolution encroached to bring dramatic change.