There are drawings of Dolbadern in the 'Hereford Court', "North Wales' and 'Dolbadern' sketchbooks of 1798-9 (T.B.XXXVIII-47, XXXIX-33 and XLVI-21, 38v, 39) but the painting is based more directly on a remarkable series of six drawings in coloured pastels on blue paper in the 'Studies for Pictures' sketchbook (T.B.LXIX-103, 104, 108, 109, 112 and 113; four examples repr. in colour in Wilkinson 1972, pp.94-5). They are all variations of the main elements of the composition, silhouetting the castle tower against the glow of the sun setting under a glowering sky, an effect rather tamed in the final oil painting. In other respects, however, the painting shows a considerable advance in drama and concentration over the more Wilsonian landscapes of 1798 and 1799, and Turner's new aspirations are reflected in the Salvator Rosa-like figures in 'period' costumes and the verses in the Royal Academy catalogue:
How awful is the silence of the waste,
Where nature lifts her mountains to the sky.
Majestic solitude, behold the tower
Where hopeless OWEN, long imprison'd, pin'd,
And wrung his hands for liberty, in vain.

The verses appear for the first time to be by Turner himself, and Owen is presumably Owen or Owain Goch, the Welsh prince imprisoned in Dolbadern Castle from 1254 until 1277, though it could also be Owen Glendower (?1359-?1416) whose final end is however uncertain; he seems to have died in hiding rather than in prison.

Turner was elected an Associate of the Royal Academy in November 1799 at the lowest age allowed by the regulations, twenty-four, though in fact he had been proposed and nearly elected the previous year. In February 1802 he was elected a full Academician and chose this work for the obligatory ‘Deposit' (now called Diploma) picture. However, he had second thoughts and subsequently offered another painting instead, but the first was chosen. Unfortunately it is not recorded what the second picture was, but it may have been something more ambitious.