The Three Tribal Thrones of the Island of Britain

• Arthur as Chief Prince in Mynyw, and Dewi as Chief Bishop, and Maelgwn Gwynedd as Chief Elder;
• Arthur as Chief Prince in Celliwig in Cornwall, and Bishop Bytwini as Chief Bishop, and Caradawg Strong-Arm as Chief Elder;
• Arthur as Chief Prince in Pen Rhionydd in the North, and Gerthmwl Wledig as Chief Elder, and Cyndeyrn Garthwys as Chief Bishop

Mynyw is modern St. David's. Dewi is St. David/St. Dewi/St. Dafyd (I've seen it spelled all three ways).

Caradawg Strong-Arm is the same Caradoc of French Romance.

The earliest fragments of the triads do not contain this triad; it is thought to have been added by a scribe in 1150 or so, in order to claim the importance of St. David's bishopric.