Celtic influence and rule over germanic peoples before roman invasi

I´m new to this group and I haven´t really gone through all the
messages yet so I´m taking the risk of bringing up an old subject
here. What I wanted to know more about and discuss more thuroughly is
the possibility of a fullscale celtic influence on germanic speech and
culture in the years before roman invasion of Gaul and Britain. I have
had a theory for at least 20 years now that some celtic tribes had had
some kind of dominion over certain parts of germanic lands in the last
millenium BC. I´m not talking about the obvious influences that we all
know (the words iron and rich) but the kind of dominance we know from
recorded history of France and Italy when germanic kings ruled over
romance folks. They steered the small kingdoms but did not influence
the way their subjects spoke much. That is my theory.

The reason for my theory comes from the odd names in old Swedish and
danish history or legend. Some names don´t fit in with the usual
germanic names but are indeed IE in origin. The oldest evidence for
iron mining in Scandinavia is from 750 BC and from all we know the
word iron is a celtic one. It´s a compelling thought, what if
archaeologists and linguists could meet on this one and either love or
hate my theory. So far, all I have discussed this with haven´t said
anything. I realize that my knowledge in either field cannot compare
with that of experienced linguists and archaeologists so I´m going to
stop there and let you decide whether my theory holds ground or can be
cast to the lions.

/Carl