Ptolemy mentions Iria as Iria Flaovia. The hypothesis I am working with is Flavia being a tautonym for Iria. Both names, at this stage, appear to mean "river": either a particular kind or "part of a river". It is just an hypothesis. Iria is too obscure: there are no occurrences enough to explain it in comparative terms: The more similar one would be Iria in Portugal, which is referred to as a river in 1142: " inter Leirenam et Heirenam rivulos".
The second term, Flavia, has been explained as an eponym of a Roman Emperor(Titus Flavius Vespasianus). As far as I could research this is quite a recent explanation and there are no classic texts to support such an hypothesis. Please do note that I haven't -I wish I could- reviewed the ancient sources. All I can say is that I am failing to confirm a Latin origin for Iria Flavia in historical sources. Or, I repeat, I could not track or found any evidence to support this Latin explanation.
So I am left with linguistic evidence only. Other occurrences do show a pre-Roman substract. Comparisons at both syntagmatic and paradigmatic levels are more easily explained from Celtic.
I would appreciate any HISTORICAL evidence of ANY toponym with the term Flavia/o being given by a Roman emperor WHEREVER in the Romania. Perhaps there is such a source and it is very well known, but I admit that I can not find it at present. I strongly, sincerely would appreciate it.
I keep my attention to flavia as a Celtic name.