Dolbadarn Castle is only 6 1/2 miles as the crow flies from the Menai Straits, and yet, the topography of the area is such that it was built by Llywelyn Fawr (Llywelyn the Great) to guard the mountain pass from Caernarfon to the upper Conwy Valley. ‘Its position at the tip of Llyn Padarn allowed the garrison to blockade anyone’s movement through that part of the north, then as now a main link to the rest of Wales. The military worth of the spot was evidently recognized as early as the 6th century but surviving masonry dates no earlier than the 1200’s.’ http://www.castlewales.com/dolbd.html
Llywleyn Fawr built the castle in the early 13th century and it was one of the last defenses of Dafydd ap Gruffydd–Llywleyn Fawr’s grandson–in 1283 after Edward had defeated Llywelyn ap Gruffydd, Dafydd’s brother (Paul Davis, Castles of the Welsh Princes, p. 42). It was then abandoned.
A visit to Google Earth reveals that the Castle sits on a crest above a slight valley, overshadowed by the enormous mountains behind it. ‘The site is a narrow outcrop of rock with steep falls on all sides, especially the east, where there is a sheer drop to Llyn Padarn’ (Adrian Pettifer, Welsh Castles, p. 33). It is likely that some kind of Roman road passed through the area on its way into the mountains, as traces remain of a temporary Roman camp further up the road, once it turns east to Betws-y-Coed.
According to Pettifer, the keep at Dolbadarn, which is the most well preserved piece of it, ‘vies with the gatehouse at Criccieth as Llywelyn the Great’s finest piece of castle architecture’. All three floors had fireplaces and toilets, even the basement. The outer walls were high enough to conceal the roof of the upper floor and protect it from being fired by missles (Pettifer, p. 34).
Llywelyn ap Gruffydd kept his elder brother, Owain, imprisoned at Dolbadarn, for 20 years, before he was released in 1277 as part of the Treaty of Rhuddlan. An old man by then, Llywelyn provided for him the cantref of Llyn, in which he died sometime before December, 1282 (Smith, Llywelyn ap Gruffudd, p. 441).
Dolbadarn Castle was last used by Owain Glyndwyr to hold prisoners during his uprising against the English crown in the 1400s. http://www.castlewales.com/dolbd.html
*Thanks to Stephen Colbert’s, Better Know a District