It is easy to assume that groups of people – tribes, clans and so on – were isolated in the Iron Age. In fact, the opposite was true – trade routes were well established connecting Ireland, Britain and continental Europe. Rome was the only game in town, spreading across North Africa, Mauretania, Cyrenaica, Arabia, Mesopotamia, Parthia, Scythia, Sarmatia, Germania, Gaul and Hispania. There was no Internet, not even a Telex or a news agency but there was the empire and its administrators, its quantity surveyors and its salesmen, purveying its values and influencing its colonies and satellites.
There was a common understanding – and appreciation – of the value of things. “Why do you, with all these grand possessions, still covet our poor huts?” was an apparent lament of the oul’ Brits when Caesar arrived in 55 BCE or something like that. I take that to mean that the Brits had some understanding of what the empire stood for and had prominent citizens and traders visiting huge cites which dwarfed their own, possibly, more humble dwellings. Big fish in small ponds suddenly made aware – but so far ignored – that there were bigger fish in larger ponds.
Anyway, inevitably, people traveled, spreading news, ideas and culture and bringing with them desirable trade items – spices, scents, slaves, ivory from North Africa used for armor (see the account of Ferdia’s armor in The Táin) while the far flung western isle had, at least, both wolf hounds and gold.
Extensive trade was long established with Gaulish Europe along settled sea routes while movement between the east coast of Ireland and what is now Scotland, Wales and England was common. Contact was probably less frequent with Greece, Scythia, Parthia, but shared knowledge – pottery, smelting – could never be unlearned while commodities like copper, tin, enamel, tortoiseshell, Tyrian purple dye from Murex glands, Falernian wine and slaves were common – but expensive – items.