These days, thanks to many decades of misinformation (and an unregulated internet), most non-Irish people (and, sadly, some Irish people) can’t tell the difference between a Gael, a Celt, a Viking, a Gaul, a Pagan/Wicca, a Skyrim warrior, a Briton, a Saxon, a Pict, blah, blah, blah, etc. etc. and if you look at many English-language representations (particularly in gaming) you’ll find that they use a mish-mash of completely different cultures for each.
I’ve recently been researching various conflicts and battles between the early European peoples and the Roman Empire and, of course, the long-term engagement between the cultures is far more complicated than you’d think. Interestingly, most of the imagery around this subject also tends to be Eurocentric in nature (the Gauls and the northern German tribes).
The above image by talented French artist Thibault Ollier, pretty much epitomises how most western people visualise those early conflicts. Applying the historical story to the reality to 1st century Ireland means a certain amount of adaptation is going to be an interesting challenge for the next book in the Liath Luachra series if I want to make it work on both a creative and culturally authentic basis.