PLINLIMMON (Plynlimmon, Pumplumon, Pttmlumon, Penlumon: Pumlumon is the name used locally: pump means five: lumon, chimney, flag or beacon; pen, head), a mountain of Wales of the height of 2463 ft., equidistant (about 10 m.) from Machynlleth and Llanidloes. Much inferior in elevation to Snowdon or Cader Idris, Plinlimmon is certainly the most dangerous of the Welsh hills because of its quaking bogs. The scenery is comparatively poor, consisting chiefly of sheep-downs (in Montgomeryshire) and barren turbaries (in Cardiganshire). If the name means " fivebeacons," only three of these are high, with a carnedd (stone-pile, probably a military or other landmark, rather than the legendary barrow or tomb) on each of the three. Plinlimmon is notable as the source of five streams three small: the Rheidol, the Llyfnant and the Clywedog; and two larger and famous: the Wye (Gwy) and the Severn (Hafren).
The morasses of Plinlimmon saw many a struggle, notably the war to the knife between Owen Cyfeilog (fl. c. goo), prince of Powys, and Hywel ab Cadogan. Here also Owen Glendower unfurled the banner of Welsh independence; from here, in 1401, he harassed the country, sacking Montgomery, burning Welshpool, and destroying Cwm Hlr (long " combe," or valley) abbey, of which some columns are said to be now in Llanidloes old church. On the side of Plinlimmon, some 2 m. from the Steddfagurig inn, is Blaen Gwy (the point of the Wye), the course of the streamlet being traceable up to Pont-rhyd-galed (the hard ford bridge), some 4 m. distant from the inn. Near this bridge are numerous barrows and cairns, on the right from Aberystwyth. There are slate quarries, with lead and copper mines. Machynlleth ( perhaps Maglona in Roman times) has Owen Glendower's " senate house " (1402), and is known as the scene of Glendower's attempted assassination by Dafydd Gam. Llyn pen rhaiadr (the waterfall-head pool), or Pistyll y llyn (pool spout), is some 6 m. south of Machynlleth. Llanidloes has a trade in Plinlimmon slates and minerals besides flannel and wool manufactures.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)