The principal evidence for settlement during the Early Iron Age (600 B.C. - 100 A.D.)
is the large number of defended hilltop enclosures (hillforts) which occur widely
throughout the area. Some of these sites have huts within them and may have been
permanently inhabited. There are two principal types of hillfort which can be identified
(a) The Bank-and-Ditch type, which occurs mainly in coastal areas, is characterised
by defences consisting of a large ditch, with the upcast heaped into a bank. This
type of fort is common elsewhere in Britain, and the Caernarvonshire examples could
have been introduced by immigrants from S.W. England.
(b) The Stone Walled type, with defences consisting simply of a massive dry-stone
wall. This could well have been built by the native population.The fact that both
types of structure occur successively on the same site (e.g., Dinas Dinorwig) shows
that there were two separate traditions.The occasional finds of decorated metal-work
are presumably imported: the Pen-y-Pass mount probably originated in S.W. England.Some
hillforts were certainly occupied into the Roman period (e.g., Braich y Dinas, Tre'r
Ceiri, Dinas Emrys).