As to the origin of this superstition, it appears to be of very ancient date. It is stated[38] that the Fenian tale, called "Cath Finntraglia," or "The Battle of Ventry," relates how Daire Dornmhar, "the monarch of the world," landed at Ventry to conquer Erin, and was opposed in mortal combat by Finnmac-Cumhail and his men. The battles were many and lasted a year and a day, and at last the "monarch of the world" was completely repulsed, and driven from the shores of Ireland. In the battle, Gall, the son of the King of Ulster, only a youth, who had come to the help of Finnmac-Cumhail, "having entered the battle with extreme eagerness, his excitement soon increased to absolute frenzy, and, after having performed astounding deeds of valour, fled in a state of derangement from the scene of slaughter, and never stopped till he plunged into the wild seclusion of this valley." The opinion is that this Gall was the first lunatic who went there, and that with him this singular local superstition originated, followed as it has been by innumerable pilgrimages to the beautiful "Valley of Lunatics" and its wells.
A visitor to this valley in 1845 writes: "We went to see Glenagalt, or the 'Madman's Glen,' the place, as our guide sagely assured us, 'to which all the mad people in the world would face, if they could get loose.' After pursuing for miles our romantic route, we came to the highest part of the road, and turned a hill which completely shut out Glen Inch; and lo! before us lay a lovely valley, sweeping down through noble hills to Brandon Bay. The peak of the mighty Brandon himself ended one ridge of the boundary, while high, though less majestic, mountains formed the other; and this valley so rich and fertile, so gay with cornfields, brown meadows, potato gardens, and the brilliant green of the flax, so varied and so beautiful in the bright mingling of Nature's skilful husbandry, was the 'Madman's Glen.' I felt amazed and bewildered, for I had expected to see a gloomy solitude, with horrid crags and gloomy precipices. Not at all; the finest and richest valley which has greeted my eyes since we entered the Highlands of Kerry is this--smiling, soft, and lovely.
"We took our leave of fair Glenagalt, and assuredly if any aspect of external nature could work such a blessed change, the repose, peace, and plenty of this charming valley would restore the unsettled brain of a poor unfortunate."[39]