D.H. New; A.L. Benjamin; K.S. Miles (February 1978). "Some features of the Aberdulais to Llandarcy section of the Neath-Abergavenny trunk road (A465)". Proceedings of the Institution of Civil Engineers. 64 (1): 153–154. doi:10.1680/iicep.1978.2747.
The three cantrefs composing Glywysing were based at Allt Wynllyw on Stow Hill (modern Newport); Nant Pawl; and Llaniltud Fawr. These were sometimes independent and sometimes controlled one another. Cf. The History Files: "Celtic Kingdoms of the British Isles: Cernyw / Glywyssing" (Accessed 14 February 2013).