Samhain, Beltane and the Celtic calendar - how much of this is actual history vs modern invention?

I keep seeing claims online that the ancient Celts believed the veil between worlds was thinnest on certain dates, and that this is why we celebrate Halloween and have all these folklore traditions around it. But I'm genuinely uncertain how much of this is backed by actual historical evidence versus modern Pagan reinterpretation.

The problem is we don't have loads of primary sources from Celtic peoples themselves - a lot of what we know comes from Roman descriptions and later medieval Christian sources, which had their own agendas. So when people talk about Samhain as this ancient spiritual doorway, how much of that is actually ancient Celtic belief versus Victorian romanticism or modern spirituality projection?

Interested in what people who've actually studied this stuff think. Are we working from solid evidence or educated guesses?

Good question because honestly a lot of modern 'Celtic spirituality' is Victorian invention mixed with wishful thinking. We know the Celts had seasonal festivals - that's documented. But the specific metaphysical claims about veil-thinning? That's largely modern spiritual practice. Medieval Christian sources were basically propaganda and the Romans were writing about foreign people they didn't understand.

The academic consensus seems to be that yes, the Celts marked major seasonal transitions and likely had rituals around them. Whether those rituals involved beliefs about spiritual realms becoming accessible? That's speculation. We're reading backwards from folklore and trying to reverse-engineer ancient belief systems, which is always dodgy.

I've read that Beltane and Samhain marked important pastoral calendar points - moving herds, preparing for winter - which would make them significant dates regardless of supernatural associations. The spiritual overlay might be human tendency to mark important dates as 'special' rather than something specifically Celtic.

Doesn't really matter if it's ancient or invented though, does it? If the date has energy and meaning for people now, that's what counts. Modern paganism isn't a reenactment society.