The most likely spot for this, simply on the basis of the strong tradition in the area, the name, and the coastal location is the Hod(d)nant which passes Llantwit/Llanillud on the Severn*, However, Hodnant is a relatively common name. There is another at Blaenporth, which used to be Blaen Porth Hodnant. There is also the Hodni stream (Nant Honddu, pronounced Hon-thi?) which runs by Llanthony Priory, and a river with the same name which runs down to Brecon to join the Usk (Visit Details). The latter was mentioned with this name by Gerald of Wales* (1197 C.E.: Book 1, Chapter II), who was archdeacon of Aberhodni (Brecknock / Brecon).

More notably, the 11th C. Life of St David* by Rhygyfarch (or "Ricemarch") (Translation) has David setting up his own School in "Glyn Rosyn ["Valley of the Roses"?], then called Hodnant". It seems somewhat coincidental that David, apparently of student of Illtud, should set up a school in a valley with the same name - possibly suggesting the Lives have been confused. David's Hodnant is generally identified as St David's on the River Alun, on the basis of the foundation being St David's monastery (Info). While there is a strong local tradition for this, the oldest evidence for religious activity in the area is a 7th-9th C. cross embedded in the wall of St Non's "Chapel" (Images), which is itself 14th C. or older, though isn't necessarily a chapel**. An alternative site might, therefore, be Llanthony Priory, which was set up on the site of an older chapel which tradition at the time (c.1103 CE) dictated was occupied by St David. The name is meant to be a contraction of Llan ddewi Nant Hoddni ("The churchyard of David in the Valley of the Hoddni")*. The oldest sites here, however, are 12th C. (including the current St David's "Chapel"*).