1911 Encyclopædia Britannica/Cader Idris
CADER IDRIS ("the Seat of Idris"), the second most imposing mountain in North Wales, standing in Merionethshire to the S. of Dolgelly, between the broad estuaries of the Mawddach and the Dovey. It is so called in memory of Idris Gawr, celebrated in the Triads as one of the three "Gwyn Serenyddion," or "Happy Astronomers," of Wales, who is traditionally supposed to have made his observations on this peak. Its loftiest point, known as Pen-y-gader, rises to the height of 2914 ft., and in clear weather commands a magnificent panorama of immense extent. The mountain is everywhere steep and rocky, especially on its southern side, which falls abruptly towards the Lake of Tal-y-llyn. Mention of Cader Idris and its legends is frequent in Welsh literature, old and modern.