In the Riad Catalina in Marrakesh I lay on my bed and marvelled at the seductive power of music. Through the window I could see the minaret of the 12th-century Koutoubia Mosque and hear the drone of the muezzin summoning the faithful to prayer with a high, keening call that floated across the rooftops.

But there was a different tune playing on my Discman: a three-minute pop song with a bouncy, irresistible rhythm. Just as the muezzin's voice has drawn worshippers to the Koutoubia for nearly 1,000 years, so it seemed appropriate that I should have been drawn here, a thousand miles from home, by another kind of song: ``Looking at the world through the sunset in your eyes Travelling the train through clear Moroccan skies'' Marrakesh Express by Crosby, Stills and Nash was one of the defining songs of the hippy era, a paean to adventure and travel. This was a song that not only made you want to hit the road, it told you where to go. I was 12 when I first heard its exhortation to "take the train from Casablanca heading south". It had taken a while but I made it.

We all follow in someone's footsteps. Graham Nash, co-writer of Marrakesh Express, was himself emulating the members of the Beat Generation - William Burroughs, Jack Kerouac, Allen Ginsberg - who in the 1950s had made a playground out of Tangier, the north Moroccan city in which the railway line to Marrakesh begins.

In those days Tangier had its own laws and administration, more than 60,000 expats and a hundred brothels. Burroughs boasted that he received "an average of 10 attractive propositions a day", mostly from young boys. But it didn't last. Moroccan independence in 1956 followed by a series of scandals brought an end to Tangier's days of excess.

My room at the Hotel Continental, a Tangier institution which opened in 1865, looked out over the port, permanently swathed in chilly mist during my day there. In the narrow streets of the medina, cobblers, jewellers and tinsmiths squatted in hole-in-the-wall shops, and old men in hooded burnouses passed by like medieval monks.

Down below, the occasional dark shape darted between the ranks of container lorries, to be pursued and chased away by lazy-eyed policemen: illegal emigrants bound for Spain. Tangier has always been a crossroads for drugs and people. It's a border town: a grey and edgy place. I headed for the new Gare de Ville on the edge of town, eager to get started.

The French built the Moroccan railway network in the early years of the 20th century, after establishing a protectorate here in 1912. One track ran east to Algeria; the other due south. As the line headed towards the Atlas mountains the harsh terrain became impassable: Marrakesh turned out to be the end of the line.

The 9am Casablanca train left on time, its red and cream carriages swaying and clanging across the points outside Tangier. I had a first-class compartment to myself, and watched as we ran through flat countryside with scrubby brown hills to one side and the Atlantic on the other. We stopped at Asilah, where a massive 14th-century Portuguese fort jutted out over the ocean; then jolted forward again. I'd been anticipating these lines from the song: "Dogs and pigs and chickens call Animal carpets wall-to-wall" But Moroccan railways have come a long way since 1969. No animals in the clean and comfortable compartment; just a fierce-looking Moroccan businesswoman in a trouser suit who sat tearing articles out of her newspaper and barking into her mobile phone. The lady got off in Rabat, the Moroccan capital - a baking grid of administrative buildings, solid, provincial and dull - and I rolled south towards Casablanca, entering the city through the shanty towns that lined each side of the track.

"Casa" was buzzing in the late afternoon, most of its three and a half million people seemingly out on the streets. Along the Boulevard Mohammed V neon lights were winking on, and an electrical crackle played above the wide, traffic-clogged avenues. Casablanca has a feverish energy. It's a place not of "sights" - there are none, save for the gigantic Hassan II mosque, which foreigners can visit only by arrangement - but of activity.

The traffic, the noise, the hawkers with their dodgy jewellery laid out on blankets in the street, the lynx-eyed girls in jeans (Casablanca is where Western travellers reacquaint themselves with the sight of the female form), the shoals of pedestrians moving as one across the street and weaving through the oncoming traffic... You get caught up in it, moving from cafe to cafe, wandering through the art deco district along streets that look much as they did 80 years ago when Casablanca was born, modelled on Marseille.

At the Restaurant au Petit Poucet velvet curtains hung above gilded mirrors and other memorabilia imported from Paris. Waiters in white jackets ferried escargots and foie gras to a mainly expat crowd. It felt like an outpost of the French empire; and indeed au Petit Poucet was the favourite watering-hole of the aviator and novelist Antoine de Saint-Exupéry on his mail flights to the Sahara in the 1920s.

His letters and doodles, scribbled on the back of the menu, are framed on the walls. The air of nostalgic, exhausted colonialism suited Casablanca perfectly. And there was more nostalgia the next day at Gare des Voyageurs station, where I found myself sharing a compartment with an elderly French couple, Simone and Jo. They were brother and sister, born and raised in Morocco but now retired to Paris and on a pilgrimage to their father's grave in Marrakesh. "J'habite en France, mais mon âme reste en Maroc," said Simone, a little sadly. She chatted animatedly in Arabic with the pushcart-boy who sold us tea and snacks.

I, of course, had my Discman out.

"Don't you know we're riding on the Marrakesh Express Wouldn't you know we're riding on the Marrakesh Expressly taking me to Marrakesh" But initially the journey was disappointing. All morning we ran through a flat dull landscape, with scrappy villages under a dark grey sky. Then at noon, as if on cue, the sun came out and everything was transformed. The countryside was now emerald green; the sky was blue, and all around we could see tiny villages of neat ochre houses, their gardens hung with orange trees.

The Anti-Atlas mountains rose up and before them lay Marrakesh sparkling in the sunshine, a medieval city on a plain ringed by snow-streaked hills. I felt like punching the air with pleasure. I'd imagined this moment many times, and I wasn't disappointed. "Quelle ville merveilleuse," said Simone.

Marrakesh, like Tangier, is another crossroads city, but one with a languid, southern air. Palm trees wave above the city walls; the air is balmy; orange blossom and hibiscus offset the blue and crimson djellabas of the locals. I trawled the shady alleyways of the medina by day, then relaxed in the calm of the Riad Catalina by night.

This was French-run, with an inner courtyard hung with greenery. Waiters brought dishes of chicken Tanjia - a Marrakesh speciality baked in a clay pot - and red Guerrouane wine; vineyards, like the railways, being another fine legacy of French rule.

Each evening I'd head to the Djemaa el Fna, the open square that for a thousand years has been a meeting place for tribes from the countryside, and home to a nightly display of music, dancing, drumming, storytelling and acrobatics. To claim, as some guidebooks do, that the Djemaa el Fna has become "touristed" is a nonsense: 95 per cent of the onlookers were Moroccan.

As the last rays of light drained from the sky the muezzin at the Koutoubia began his long, mournful wail. Behind the minaret the sun was setting in a sky of gold. "All-ahh ak-bar", droned the muezzin. "Had to get away to see what we could find," sang Graham Nash, in my head. The light died, the crowds grew quiet, and all was well at the end of the line in Marrakesh.