The Celts in Brittany, was an amalgamated culture. It principally acquired their symbols from religious negotiations with other Kelts. The symbols where officially recognized amalgamations of icons (religious representations).
When a religious icon was deemed to work well during trade, it was then kept because it brought prosperity to those who used it. The knowledge of prosperity gave these bronze age people an easier life; hence, it was found suitable to represent what the various Celtic religions held in common as holy: “knowledge, trade, culture and religion – used to prosper…”
Because Bronze-Age, Celtic religious icons had been found suitable for prosperity’s sake, it had once again been found suitable enough to represent them again even during the Christian conquests. All those concerned, continued prospering in religious knowledge, as in trade…
N.B. Taken and adapted from Wikipedia, the free encyclopedia, and from a French website on the Brittany culture: