If you look for the Green Man on the internet (as with popular books), most people you will find who discuss this allegedly mythological figure will tie connections between High and Late Mediaeval grotesques and some Imperial Roman art, which is fair enough, and then often run off telling you about vaguely similar things in other cultures and then trying to convince you that Bacchus is Okeanos is the Green Man. It’s all a bit breathless and doesn’t really work.
One can reasonably demonstrate that the visual motif in Roman art is about the same thing we’re getting on mediaeval cathedrals. No dispute there. The links with Bacchus and Okeanos, however, are tenuous at best.
However, to say that a motif from pagan art is because the sculptors themselves were still pagans is a bit silly. All sorts of magnificent, wonderful, bizarre things are going on in mediaeval churches. These are the things that lurk about in the edges of the consciousness of the human mind. Things go bump in the night. Man is a creature of Earth, even if he can look to the heavens. We are physically of the same stuff as everything else. And so things make their way onto church walls and pillars and roofs, not only Green Men but other, stranger figures.
We like to parse the world of wonder and mystery in our Enlightenment world. And so there is nature and, perhaps, super-nature. But living with the inheritance of the thought-purges of the Renaissance and Reformation, super-nature is God and his angels, and — depending your mood — the devil and his minions. Full stop.
That mediaeval people may have believed in other facets of the numinous world makes them no less Christian than we. It means that their universe was larger in many ways. Indeed, it is not the Green Men who make you pause and question the level of Christian commitment held by the mediaeval world so much as the Platonic worldview so many held!
However, for me, the idea of a visual motif from the pagan world surviving into the Middle Ages cannot mean that these people were half-Christianised pagans (although some/many of them likely were). This is partly because Peter Brown has aptly and amply demonstrated that the Cult of the Saints is not a paganised version of Christianity, even when it so strikingly resembles paganism (see The Cult of the Saints: Its Rise and Function in Latin Christianity).
A second reason is the fact that the mythology neo-pagan websites attach to the Green Man is extrapolated entirely from the architecture itself. We know nothing of what a stonemason in 13th-century York was thinking when he carved a Green Man. All we have is a visual motif that bears a resemblance to a Roman pagan visual motif. To tie it in to Druids and pre-Christian Germanic religion and specific ideas about humanity’s relationship to nature — we cannot go this far. The evidence is unable to bring us to these conclusions, because the Classical framework wherein our first properly attested Green Men arise gives us no such help and is so philosophically plural that there is no single Graeco-Roman pagan vision of humanity’s relationship to nature.
A third reason why the Green Man does not proclaim to me that these people were still pagans who worshipped whatever it is that pagans worshipped is the fact that we know full well that an angel is an angel, and not the goddess Victoria (Nike) or Cupid. Yet more than enough art shows angels who resemble one or the other. Motifs from pagan art carry over into Christian art to a very large degree; this is the classical inheritance of the mediaeval world. It comes along with allegorical readings of texts, Ptolemaic astronomy, dactylic hexameter, and Ciceronian rhetoric. For a good, readable treatment of the mediaeval and Renaissance use of classical pagan literary and philosophical ideas, read C S Lewis’ The Discarded Image.
Third, Green Men appear in churches. Mediaeval piety as represented by illuminated manuscripts, the rest of church architecture, Books of Hours, Breviaries, the Cult of the Saints, the Cult of the Cross, the Cult of the Virgin, Corpus Christi festivals, mystery and miracle plays, devotional poetry, and eucharistic devotion shows me people who have a strong Classical inheritance, sometimes (even among the ‘elites’) un-Christian and pagan, but always overlaid and refashioned and reinterpreted in light of the Christian message and Christian gospel.
Green Men tell me nothing of survivals of pagan piety into the Middle Ages. And they tell me nothing of ancient pagan beliefs about nature. For that, I will turn to Lucretius or Marcus Aurelius or Plato or Aristotle. They do, however, tell me of the survival of pagan artistic motifs of one form or another through the Middle Ages. And this I already knew.
One final thought: perhaps these modern re-imaginings lie in the false dichotomy forged between popular religion and the elites by David Hume. Peter Brown deals with this is in his opening chapters ofThe Cult of the Saints. Perhaps that is precisely the problem. We see the monks as cut off from these barbarians who, through forced, mass conversions never actually abandoned their old religions. In some ways, that is a story Northern Europe tells. However, this is not the story of the Mediterranean in Late Antiquity, the place where our Green Men have their best earliest attestation.
So much for now. I think we should re-think the Green Man as a pagan visual motif surviving in a Christian setting. This may give us a thoroughly different narrative.