"We know that the latest archaeological expression of the pre-Roman European Iron Age, the so-called La Tène culture, lasted in a vestigial form in Ireland, where there was no Roman occupation to swamp it, until at least the time when the introduction of Christianity in the fifth century brought its considerable changes in intellectual and to some degree social organization and particularly in art styles and motifs. I shall attempt to show that the background of the Irish epic tales appears to be older than these changes, and hence that when all due allowance is made for later accretions the stories provide us with a picture -- very dim and fragmentary, no doubt, but still a picture -- of Ireland in the Early Iron Age."
Waddell, however, offers a much more nuanced view: "It is questionable whether early Irish epic literature is a window on a prehistoric Iron Age, as Jackson once claimed...for...some descriptive detail of motifs such as the sword [and chariots-ed.] and the use of silver and other precious metals in the tales of the Ulster Cycle reflects the contemporary world of the later redactor." (Waddell, John, Joe Fenwick, and K. J. Barton. Rathcroghan: Archaeological and Geophysical Survey in a Ritual Landscape. Dublin: Wordwell, 2009. 28.)
In his 2008 translation of the Tain, Ciaran Carson argues "Whether or not it is an Irish Iron Age is another question. For instance, it is undeniable that the social and warfaring practices embedded in the narrative bear remarkable similarities to those of the Gauls or 'Celts' of continental Europe, as described by Diodorus Siculus in around 60 BC..." (Carson, Ciaran. The Táin: a New Translation of the Táin Bó Cúailnge. New York: Viking, 2008. xx.)