[If the text below uses any of the terms ‘hill-letter’, ‘river-letter’, ‘old-style name’, ‘transitional name’ and ‘inversion-type name’ a reader who is not familiar with those terms may wish to refer briefly to ‘The Celtic names of hillforts’, where an explanation of those terms is given].

The Celtic names of hillforts

Caer Dynnaf

Location: just west of Cowbridge, Glamorgan

OS map reference:  SS 984 743                                         

Celtic name:  perhaps Bomio, but possibly Bomvio, Bomivo or Bomido

Source:  Antonine Itinerary (Iter XII) – Bomio

This hillfort stands on a high hill with a steep drop down to the river Thaw at a point opposite Cowbridge. The hillfort does not appear from the OS maps to be built only on the summit of the hill, but to extend some way down the southern, eastern and western slopes of the hill.

The name Bomio is a straightforward old-style name in the hill-letter m, bom meaning ‘high hill’. The name Bomio appearing in the Antonine Itinerary will refer to the Roman town at Cowbridge itself, the name simply having been transferred from the hillfort. The writer’s reasons for identifying Cowbridge as Bomio are given in the entry for Bomio in the Alphabetical List. But whilst Bomio was most probably the Celtic name of Caer Dynnaf, there is another hillfort a little to the east of Cowbridge, at Llanquian Wood. This hillfort is built on the side, the slope of a high, steep hill, so one might expect to see a c/g and v in the name as well as a b – in other words the name of this hillfort was probably not as simple as Bomio.  Bomio is assumed here to have been Caer Dynnaf simply because this hillfort is very much nearer to Cowbridge than is that in Llanquian Wood, but the archaeologists could put the matter beyond doubt if they could demonstrate convincingly that only one of the two hillforts was occupied at the time of the Roman advance into this region. The Celtic name may have been Bomio, or possibly Bomvio or Bomivo, the v referring to the fact that the hillfort was built on a slope, or even Bomido (in the case of Caer Dynnaf), the d referring to the fact that the hillfort was at the top of the hill, even if it did extend some way down the slope.