In Isfahan, mist-blue and melon-green tulip domes bloom in the desert, and indigo mosaic monuments rise above lines of white poplars. I am on my way from Istanbul to India, tracing the route of the Asia Overland "hippie" trail.
In the 1960s and 1970s an optimistic generation, travelling in ancient Austins, rainbow-coloured double-deckers and fried-out VW Kombis, hoped that this great journey would lead to a better world. Many of them paused here to appreciate this splendidly proportioned city. The English aesthete and travel writer Robert Byron described Isfahan's sublime beauty as bringing a "rare moment of absolute peace, when the body is loose, the mind asks no questions, and the world is a triumph".
In the soft light of late afternoon, the immense Imam Khomeini (formerly the Royal) Square spreads beyond a vaulted, labyrinthine bazaar. Its two great mosques, with their majestic, recessed portals flanked by minarets, are positioned in near-perfect symmetry with the buff, brick Ali Qapu Palace. I walk the half-kilometre of the maidan's length beneath tiered arcades the colour of pale honey, among ice-cream vendors, tourist calèches and picnicking families. Fathers and sons gnaw on cobs of char-grilled corn. Mothers laze on tartan rugs, loosen cumbersome chadors, offer a glimpse of red hem or tight denim. Daughters release long braids of brown hair from beneath their scarves, then wade barefoot in the fountains. Byron wrote that the square's beauty lay in the contrast between a formal space and a romantic diversity of buildings. I am reminded of both St Peter's in Rome and the soaring Palais des Tuileries in Paris, burned by the Communards in 1871.
Ahead of me is the Masjid-i-Shah mosque, the culmination of a thousand years of Persian architecture, virtually untouched since its completion in 1638. Almost the entire surface of the vast, airy building is covered with exquisite glazed tiles. Swallows sweep across its tranquil inner courtyard, the arc of their flight as elegant as the line of receding arches. In a sunken porch, two schoolgirls sketch the intricate arabesques, adding dark-blue and golden-yellow watercol our, re-rendering the inscriptions. A caretaker arrives on an old bicycle, his reflection rippling in the wide ablutions pool.
In this serene space, unspoiled by the modern age, I consider the legacy of the 1960s travellers. Only a generation ago, English girls hitch-hiked alone across Iran. Free-spirited teenagers from Berlin and Boston were welcomed as honoured guests in Baghdad. The hundreds of thousands of footloose westerners, in flares and open-toe sandals, may have been the first movement of people in history who travelled to be colonised rather than to colonise. But their values and comparative wealth did change the places they visited. The host societies, especially those of rural Iran and Afghanistan, were for the most part defiantly conservative. I begin to wonder if the casual morality and humanism of those first independent travellers could have further polarised these countries, encouraging urban liberal minorities while insulting - even enraging - traditionalists and zealots. Might this not even have helped to stir the stern Islamic reawakening?
"Hey, mister, where are you from?" shouts a bold young man, shattering my thoughts. I ignore him, walking away from him and his friends. He calls after me again. "We are Pink Floyd fans."
This I had not expected.
"The lunatic is in my head," he quotes, arresting my step. "You lock the door, and throw away the key. There's someone in my head but it's not me."
All four men are engineering students from Mashhad, over on a study visit. I know from my research that a ring of weapons and defence industries, including the new Isfahan Nuclear Technology Centre, surrounds the city. The men are in their late teens, their skin pale from in-door lives, wearing clean white shirts and black slacks. One of them carries the latest issue of the Ferdowsi University magazine, Fanoos Khial (or "Lantern of Dreams"). It features a six-page article on Pink Floyd.
"We know all about Roger Waters."
"And Steve O'Rourke going to that great gig in the sky."
Their knowledge of the band is better than mine. They gather around me, excited to show off their pop-music expertise, telling me that a previous issue of the magazine was devoted to Dylan interviews and reviews.
"Hey mister, what is the song at the end of Dark Side of the Moon?" I am asked.
"If you listen to the very end of 'Eclipse' and turn the volume up really high, you can hear faint music."
"'Paul is Dead'?" I suggest.
"Some people do think it's a Beatles number."
"I heard it was classical music."
"Do you know these songs are over 30 years old?" I ask.
Then, in the vaulted main sanctuary, standing on a black paving stone under the great dome, the four young men start to sing: "And if your head explodes with dark forebodings too . . ." Other visitors stop and stare. Old men dozing in the cool of the madrasa sit up on their blankets. ". . . I'll see you on the dark side of the moon."
I am shaken by their display, anxious of its impiety. I feel I have been denied my moments of reflection and "absolute peace". I am aware more than ever of the long shadow that the 1960s and 1970s cast over our fearful and protective era.
As the clear echo reverberates a dozen times around the sanctuary, a stranger pushes forward, not meeting our eyes. He puts down his mobile phone and, as if to nullify the men's irreverence, chants up into the dome, "Allahu akbar" - God is great. Now his words ring around the dome.
The agitated caretaker is at our side, hissing at the students in Farsi, shepherding them out of the mosque. "Mister, you know there is no dark side of the moon really," one calls back to me, paraphrasing Pink Floyd's lyrics. "It's all dark."
Rory MacLean's book "Magic Bus: on the hippie trail from Istanbul to India" is published by Viking (£16.99)