If it served the Welsh princes as a refuge, it was also of use to them as a prison, in which they could hold their most dangerous adversaries, and the tower of Dolbadarn at the foot of Llyn Peris was their gaol. The most noted of those who were there confined was Owen the Red, brother of Llewelyn ab Gruffydd. On the death of David, son of Llewelyn the Great, in 1246, the Welsh of Gwynedd chose the brothers Owen and Llewelyn as joint kings to rule over them and lead them against the English. It was an injudicious choice, for in Wales in a royal family a man’s worst foes were those of his own household, and the electors might have foreseen that these brothers would ere long fly at each other’s throat. The two princes had a brother David, who was dissatisfied at being left out in the cold, and he hasted to the court of King Henry III. to obtain his assistance against his successful brothers. The King was delighted to have an excuse for fomenting fratricidal war in Wales, and he flattered and encouraged David, who began to intrigue with Owen against Llewelyn. Suddenly, in 1255, these two brothers raised the standard of revolt, but Llewelyn was on his guard, and he captured both of them and slew many of their followers. Owen, as the more dangerous, was sent to Dolbadarn, and was immured there for twenty years; but David was liberated in 1258, as he feigned the profoundest contrition. [Illustration: ABERGLASLYN PASS] But David only waited his opportunity, and he entered into a secret arrangement with Owen, prince of Powys, to murder his brother Llewelyn, so that he might secure the crown of Gwynedd. In order to further this plot, David recommended Llewelyn to invite the prince of Powys to a great banquet at Aberffraw, to be followed by hunting parties in Môn. This was in 1275. Llewelyn, unsuspecting treachery, agreed. Prince Owen arrived, but his retinue, on which he relied for obtaining the mastery of the palace, in the confusion consequent on the murder, was detained by bad weather and the impassability of the roads. David was alarmed. He suspected that Owen of Powys purposed betraying him, and he took to flight. Llewelyn, perplexed at the disappearance of David, questioned Owen, who made full confession of the plot. The conspirators intended to have surrounded the bedroom of Llewelyn in the night, and to have assassinated him in his sleep. The Prince of Wales, on learning all particulars, cited David to appear before him and answer to the charge of high treason; but David declined to attend, and, collecting a body of armed men, fell on and ravaged portions of his brother’s territory, and when Llewelyn marched to chastise him he fled to the court of Edward I., who received him favourably.