At the accession of William Rufus the domain of Gwynedd had been reduced to Anglesea and the Snowdonian district, and that of South Wales, or Deheubarth, to the lands contained in the basins of the rivers Towy and Teifi, known as Ystrad Tywi and Ceredigion.
As an important outpost in the upper valley of the Teifi, Lampeter possessed a castle, which was demolished by Owen Gwynedd in the 12th century.
In 1169 Owen Gwynedd died and was buried in Bangor cathedral after a reign of 33 years, wherein he had successfully defended his own realm and had done much to bring about that union of all Wales which his grandson was destined to complete.
The old British fort, Caer Drewyn, one of a chain of forts from Dyserth to Canwyd, is the supposed scene of Glendower's retreat under Henry IV., and here Owen Gwynedd is said to have prepared to repulse Henry II.
Mold Castle was probably built by Robert Monthault (temp. William Rufus), was taken and destroyed by Owen Gwynedd in 1144-1145, its site lost to the English and retaken by Llewelyn ap Iowerth in 1201, and by Gruffydd Llwyd in 1322.
At the castle of Cardigan in 1176, Prince Rhys held a historic bardic entertainment, or eisteddfod, wherein the poets and harpists of Gwynedd and Deheubarth contended in amicable rivalry.