Historians agree that we actually know very little about the religion of the various Celtic peoples who inhabited these islands before the Romans arrived. We know that the druids were a sort of priestly sage, and that their duties included augury and human sacrifice; they seem to have had a link with oak trees; much more than that is speculation. Disappointingly, there is absolutely no solid evidence linking them with Stonehenge.
Tomorrow's festival was invented in modern times by Iolo Morganwg, a patriotic Welshman with a frenzied imagination and a penchant for forging ancient documents. He celebrated the first "Gorsedd" in London, on Primrose Hill, in 1792. Like so much of what we now think of as Welsh tradition, the Gorsedd was a creation of the Romantic Age.
Philip Shallcrass, a contemporary Druid, disarmingly admits our historical ignorance, and indeed welcomes it. "We know so little about what druids got up to in the past that we are free to concoct just about anything and call it Druidry today," he writes in a volume entitled Paganism Today. Indeed, one of the few beliefs shared by contemporary Druids is that doctrinal tolerance is important; for their attitude to theology is highly individualisticand undogmatic.
But if there is one other fundamental Druid tenet, it is that nature is sacred. Tomorrow, the worshippers at Stonehenge will pray to the rising sun, and honour the sacred oak tree. It is at this point that orthodox Christians begin to feel uneasy: surely this is pure pagan idolatry. "Claiming to be wise, they exchanged the glory of the immortal God for images resembling mortal humans or birds or animals or reptiles," as St Paul put it in Romans. The Druids, in their turn, will make light of the Christians' anxiety; it seems typical of a religion that exalts the spiritual, but fears and denigrates the material world.
Caricatures conceal as much as they reveal. It is not clear that all modern Druids make idols of nature. Many of them have even considered themselves as Christians. Philip Shallcrass tells us that "Most Druids . . . believe in some kind of unified spiritual force underlying the manifest world." And Christians would share their belief.
On the other hand, the portrayal of Christianity as a religion hostile to the material world is deeply misleading. The Bible begins with the creation of the heavens and the earth, and God sees that each thing is good. In the incarnation, Christians believe, the Son of God identified himself fully with a flesh-and-blood human being.
Most Christian ritual is highly sacramental: the elements of the natural world become signs of the presence of God. Finally, the restoration to which Christians have traditionally looked forward is not only spiritual, but also material: the resurrection of the body and the renewal of heaven and earth.
Caricatures distort; but they distort an underlying reality. It is true that Christianity inherited from Judaism a passionate opposition to idolatry, and a deep suspicion of anything that suggested nature-worship. We need to be clear about the real reason for this. This was not because Jews and Christians thought that the created world was evil. Indeed, Christians have argued vehemently for its goodness against dualist groups such as the Manichees. The point, rather, was that it was created, the handiwork of the Creator.
For the Jews had made the greatest theological discovery of all time. They had come to understand what it means to claim that the Lord of Israel made heaven and earth. God is not simply a larger, more powerful, member of the universe, one of us but bigger. God is the source of everything that is. Any less than this - any limited being whom we could claim for ourselves, or manipulate, or even comprehend - is not God.
There is indeed a cosmos; the visible world does have a unity and an order, a meaning and a purpose. But that is true because its source and goal is the one Creator. In other words, the Christian attitude to creation is twofold. Creatures are not God, that is why they are not to be worshipped. But their source is in God, and that is why they may reveal his holy presence.
For many centuries Christians themselves held celebrations at midsummer. On the feast of John the Baptist they lit bonfires and asked for blessings on their cattle and crops. The Protestant establishment, fearing magic and superstition, put a stop to the fun. Perhaps, though, they should have trusted the people's instinct for natural signs.
The world, because it is created, is sacramental. That is why the sun so fittingly symbolises the power and beauty and energy of its life-giving Creator.