According to Italian anthropologist Augusto S. Cacopardo, we've been celebrating Samhain for a long, long time now.
Some 6500 years ago, a group of people speaking a family of related dialects called Proto-Indo-European lived in the grasslands between the Black and Caspian Seas. In time, they expanded east and west into Asia and Europe, bringing with them their language, ancestral to many South Asian, and most European, languages, including the one that you're reading now.
In his book Pagan Christmas: Winter Feasts of the Kalasha of the Hindu Kush (2010) Dr. Cacopardo contends that they also brought with them a festival called *Semen(os), the ancestor (and namesake) of our modern Samhain.
Of this festival Cacopardo writes, [T]hough it may not have marked the beginning of the year, it seems to have some traits of a New Year feast, or it must have opened, at any rate, the winter period (260).
He adds: It surely marked, however, a time considered to be particularly numinous because gods and fairies came close to human beings. It coincided with the time when the herds were brought back to their winter quarters and it marked the beginning of the winter sacrifices (260n51).
Although the meaning of the PIE name is not entirely clear, it would seem to derive ultimately from the root *sem-, “summer.”
Well, now. I myself have not yet tracked down Cacopardo's sources, so just how convincing the evidence for *Semenos may be, I can't say. Watch this blog.
We've long known that Samhain is ancient. The Mound of Hostages (Dumha na nGiall) at Tara in Ireland, begun circa 3500 BCE—where in historic times a pan-Irish Samhain was kept—is oriented to Samhain (and therefore also Imbolc) sunrise.
But maybe—just maybe—it's even older than that.
So, how do you say “trick or treat” in Proto Indo-European?
Semenos mânos: Good Samhain to you and yours.
Above: Engraved orthostat, Mound of the Hostages
Tara, Ireland (circa 3500 BCE)