1. "Cerrig Cyfammod Glyndwr - Glyndwr's Covenant Stones.
Two unhewn blocks of white quartz, almost certainly placed with intention, with a small natural outcropping boulder midway between them, to which the local tradition points as marking the site where Owen Glyndwr 'held parley, and made his covenant.' The boulders are on the north-western slope of Plynlymon, 100 yards above the right bank of the river Hyddgen, and in a shallow depression between Carn Gwilym and the carneddau on Banc Llechwedd Mawr. They are not marked on the Ordnance Survey sheet. Each stone is two feet high, and shows no trace of tooling. They are 60 feet apart and are aligned exactly north and south. Though not placed in an elevated position, they can be seen from afar, and show up conspicuously in the sunlight. - Visited, 6th May, 1910."
Source: RCAHMW Inventory: Montgomeryshire, 1911; no.921.
B.A.Malaws, RCAHMW, 21 February 2006.

2. Two irregular quartz blocks, known as 'Cerrig Cyfamod Glyndwr' (Glyndwr's Covenant Stones), are set 31m apart on gently sloping moorland in the valley of Afon Hyddgen. The stones align with a third (nprn 303680) on the skyline, some 1100m to the south.
Source OS 495 card: SN78NE6.
J. Wiles and B.A.Malaws, RCAHMW, 19 January 2005.

3. The two quartz blocks were visible when visited in 2005. They are on a NNE-SSW alignment, 31m apart. The southernmost stone is the larger of the two, measuring 1.2m by 1.1m and 0.7m high. The northern stone measures only 0.8m by 0.7m, by 0.4m high. The origin of the tradition associating the stones with Owain Glyndwr's victory at the Battle of Hyddgen is unknown, and it seems unlikely that two small stones of this kind would have been placed to commemorate a battle site. They may be erratic boulders.
R.P. Sambrook, Trysor, 06 January 2005.

4. As stated in reference 1 above, the tradition is that these stones commemorate the site where Owain Glyndwr made his covenant, and not the site of the Battle of Hyddgen, which it is believed may have taken place some distance to the north (nprn 402310).
B.A.Malaws, RCAHMW, 21 February 2006.