The Votadini exodus to Wales

[Agraes]

In a more simple fashion, I would simply see the draco used by Sarmatians AND Romans and well attested in use quite late in Britain (see the Bayeux Tapestry) as beeing the possible origin of the welsh dragon.

But for the case of Gwynedd, it would like to add that in its territory lies Segontium, the very likely fort of the Seguntienses we find in Illyria according to the Notitia Dignitatum near the place where Magnus Maximus died in 388 AD, and I seriously don't think its a coincidence and Im not convinced by the iberian Segontia theory to explain their name. And the emblem of the Seguntienses are two red worms.

As a reminder, here they are rendered on our scutii, the head beeing reinterpreted from another source.