It is simply that the monks here run their own republic, under licence from the Greek state. It has its own rules and passports. Everyone must arrive by a special ferry. Almost everyone living on Athos is a monk, but more that that, almost all of them, almost all the time, live their lives according to a tradition which in its main habits of thought and practice is 2000 years old. This is where perhaps 1500 Orthodox monks ö mostly Greek orthodox monks ö live in twenty monasteries and perhaps twice as many again isolated cells, hermitages, and micro-monasteries of two or three men. Some of these latter are perched in cliff-faces where goats would fear to tread and at the feet of which there is that amazing fish-filled sparkle of the gin-clear sea. OK in summer, an old monk told me. Hellish in winter.
Athos is in Thessalonika, in northern Greece. It is one of three peninsulas of land, the Chalcidice, which stick into the Aegean like the fingers of a mutilated hand. They are about forty kilometres in length. Athos has a tall spine running most of its length. It is densely and gorgeously wooded. It ends in a giant mountain, Mount Athos, whose tip sparkles like marble. There are so many trees on Athos because there are no females. That is, there are famously no women, but there are no female domestic animals either, so there is none of the over-grazing which is the curse of the Mediterranean. In truth, there are some females, because I have seen plenty of kittens gambolling in the sunshine of the ten or so monasteries I have visited on Athos. And there are of course no restrictions on the sexual habits of the bees which swarm all over Athos, spreading the pollen of wild flowers so that the whole place ö especially after spring downpours ö bursts with colour and scent.

The humans here have one business they think matters: Christianity old-style. A monk on Athos once sat on the end of my bed in a dormitory of the kind Charles may now be sleeping in, and told me that he knew, and he meant knew, that demons are real. For him, Athos was a 'spiritual desertä: a place where a man should escape the cityâs civilising corruption and do battle with the Devil, man-to-man, in the stillness of the night, without domestic comforts to distract him. That monk left me as bedtime reading a printed account of his own Abbotâs battle with these horrors: 'Just as we read about them in booksä, he wrote, 'I beheld them exactly like that: dark, with their tails, their horns, their glaring eyes thus wide open.ä The writer was actually young and educated, and very businesslike. It is the knack of the Orthodox way to combine the practical and modern with the ancient. That is perhaps why Charles has been drawn to this branch of the faith, and to the music of John Tavener, the British composer who has embraced Orthodox chant, in which style he wrote a hymn which was used at Princess Dianaâs funeral. Earlier this year, Charles attended the premier of Tavenerâs huge new choral work, 'The Last Discourse'.

The night I was told about the demons, I am afraid to say that I slept like a baby, as I always did during my two stays on Athos. The monks only let you stay a week or so, and I walked everywhere, along cobbled paths which were once used by the monks and their donkeys. I was caught between wanting to stay and contemplate in this or that exquisite place, and wanting to see the next monastery, to taste its particular delight. I especially liked the different food I was served. Vile, was the verdict of most western European travellers in the last couple of centuries. Not a bit of it, I thought: a little raw onion, a clove garlic, an apple, these were the things beside oneâs plate. And then there might be a little mess of bean stew, or thick, sweetened yoghurt. Pitta. Perhaps a glass of fizzing retsina, home-made, to send your head reeling. You see, even spiritual tourism has its dilemmas. And to tell the truth, I cheated more than somewhat. The best cigarettes I ever smoked were strong little Greek jobs, in the evening, on a wall somewhere, after the last prayers of the day, with a fellow pilgrim, before turning in ready for prayers at four am in the morning. And what prayers! Deeply male murmurings from tall, serious men in musty black serge, their whispy hair down in pony tails and buns, with incense, and candle flame glowing back from icons dripping gold and telling all the familiar bible stories and the stories of obscure saints. I was always told that pilgrims werenât allowed on Athos during Orthodox Easter, when laurel leaves are strewn everywhere. It falls this week, this year, so Charlesâ visit now may indeed be a special privilege.

Anyway, he is now sharing spirituality of a tough, almost peasant, kind. Its heroes for a thousand years have been simple men of amazing ruggedness, many of them ignorant of letters. For around a thousand years, Athos has been devoted to creating and nurturing these 'spiritual fathersä and their unadorned devotion to prayer interpersed with fishing. The best known of them never became leaders of men: it was often their own aristocratic or educated admirers who recorded the old boysâ simple messages and reinspired whole monasteries with them. Of course in practice, there was laxity on Athos, too. Specially in the early and middle years of the last century, apparently. Numbers had drastically declined from their peak of about 7000 in the 19th century. Monks lived under a rather light rule, in small groups. 'They ran it more like a gentlemenâs clubä, one monk told me. I rather like the picture, having seen amiable, bumbling old Athonites living out pleasant last days amongst their cats and vegetable plots. Then in the 1970s and 1980s, Athos underwent something of a revolution. Young educated monks came to the place and began to take over. Some of their number have begun to feel they were a bit brutal with the old men and their ways. But these youngsters were ardent and fundamentalist about the rigours of prayer and meditation. They also believed in communicating with the outside world a bit more. And they believed in restoring full-on monastic, community, life to the crumbling spiritual barracks they took over.

If nature is wonderful here, the architecture is even more so. Athonite monasteries are huge, and obviously built to house hundreds of people. Best of all, they have amazing verandahs which poke out several storeys up above ground. At Simonos Petra, for instance, there is a rickety balcony which seems to move with every footfall, and yet we were supposed to stand and discuss religion here. I have rambled round monasteries built for hundreds of men, in which now barely a handful live. They are a sort of spiritual Marie Celeste, except one was just as likely to come across a cellarful of skulls, all heaped in an orderly way, and all labeled ö liked tattooed skin-heads ö with the name and dates of the previous inhabitant of that brain. Or here, there is a workshop, with the nineteenth century tools which were used to build furniture or frames for icons. I doubt even the reformers have managed to change much of that.

The new young men, themselves now headed for middle age, brought jeeps and new forestry techniques to Athos. The old donkey paths were sometimes allowed to fall into disuse, and became overgrown. Some of the youngsters seemed too busy for their own good. But Charles wonât have to worry about any of that. His father, Prince Philip, has visited Athos, and now Charles is drinking doubtless in the same extraordinary atmosphere. The monks of Vatopedi, his chosen monastery, will surely have laid out the red carpet for him. But it will probably be threadbare, and I have little doubt that Charlesâ experience will be quite like that I and thousands of others have been allowed there. A privilege indeed.

Richard D North is the media fellow of The Institute for Economic Affairs