The Nuttall Encyclopedia
A giant, prince, and astronomer of Welsh tradition, whose rock-hewn chair on the summit of Cader Idris was supposed to mete out to the bard who spent a night upon it death, madness, or poetic inspiration.
Wood, James, ed. Entry for 'Idris'. The Nuttall Encyclopedia. https://www.studylight.org/encyclopedias/eng/nut/i/idris.html. Frederick Warne & Co Ltd. London. 1900.