Thanks! The Celts had craft of their own (they were the first to make a single-piece wagon wheel rim, for example), and trade results from having any two people (or towns, or tribes) wanting something without having to fight for it.
http://www2.iath.virginia.edu/Barbarians/first.html
there is a brilliant graphic of a wagon on this website somewhere...but I can’t find it again, I find the site difficult to navigate.
Something about it reminded me of the peasant (Bauer) wagons of Bavaria.