As DERW is the Welsh for oak the name was thought to mean 'Oak Grove' or 'Place of Oaks'. According to historical documents in the National Library of Wales, Aberystwyth, the first of the name was Gruffydd Derwas (Gruffydd of the Oak Grove) of Cemmaes, Esquire of the Body to Henry VI, 2nd son of Meurig Llwyd, 6th Lord of Nannau. At this time Powys was also known as Cemais in English and Cemmaes in Welsh. His elder son Howel Sele, 7th Lord of Nannau, was reputedly killed by his cousin, Owen Glyndwer (or Glyn Dower) who then hid his body in a hollow oak tree in the grounds of Nannau. Some forty years later a skeleton, corresponding in size to that of the missing man, was found in such an oak. The tree remained until 1813, when it fell on a still July night soon after being sketched by the antiquary Sir Richard Colt Hoare, who said it then measured 27 feet in girth.
This Gruffydd Derwas was the great-great-grandfather in the maternal line, of John ap Owen (alias Derwas) the ancestor of the Derwas families of Penrhos and Penrhyn, whose will was proved at St.Asaph on 14th November 1577, his mother Anne Say being the daughter of Elen Derwas of Cemmaes, granddaughter of the said Gruffydd. His paternal great-great-grandfather was Sir Gruffydd Vychan of Garth in Guilsfield, the second son of Griffith ap Evan ap Madoc ap Gwnwys, who was 18th in direct descent from Brochwel Ysgythrog, a 6th century King of Powys.
As the word for 'grove' is celli it is thought the name Derwas could be a corruption of English/Welsh 'as oak' and to mean 'men of oak'. This thought is now superseded by the Gaelic word 'as' meaning 'out of ' giving a Welsh/Gaelic meaning of the name as 'out of oak'.
The start of the 'family' can be claimed as Vortigern and the family tree prior to the year 404 on the assumption that Cadeyrn, King of Powys started his family with Cadell when he was twenty. The 'tree' of his descendants is reproduced above and notes follow on any interesting members, so far as can be traced.
It is known that when the Romans started withdrawing in the early 400's Cunedda, from the Scottish borders, marched south with his army and settled in the north and Cardigan Bay area, where he set up kingdoms for each of his six or seven sons, naming the areas after them. As previously stated a tomb to 'Cunorix', which could be the Latin for Cunedda was found at Wroxeter. If the sight at Wroxeter was abandoned as a memorial to Cunedda, this could be why the township of Amwythig (Shrewsbury) was started close by.
Ancestry of the Derwas family can be traced back to Vortigern (meaning High King) left by the Romans as the main ruler of Britain. His oldest son Cadeyrn Fendigaid was made overruler of Wales and the West Midlands and in turn his two sons, Cadell and Rhyddfedd, were made Kings of Powys, covering all of North Wales. Rhyddfedd had no family but Cadell had 8 sons and 2 daughters. It is thought that 6 sons perished early, the other two becoming Kings, namely Tegid and Cyngen. Our direct tree is through Cyngen - King of Powys, King of Teyrnllwg, born about 430, he was founder of the famous Monks' College of Bangor-Iscoed, whose seat of government is thought to have been situated at Pengwern (later called Shrewsbury), [see previous Pengwern paragraph], and whose palace is thought to have been situated on the site of old St. Chad's and to have extended as far as the present site of Aston's Furniture Store.