Nirvana, by way of Ancient Greece

In a remote, mountainous region of Pakistan there sits a Buddha wearing a toga. He is part of the remains of a great, lost culture initiated by Alexander the Great

It was evening late last Autumn. Walking in the hills of Pakistan near the Afghan border, I found myself climbing up a goatpath in Swat, one of the most beautiful valleys in the North-West Frontier. Here, the snow peaks of the Karakorums widen and thaw into a landslide of paddy- fields and cultivation terraces. Below, the Swat river - in autumn the colour of lapis lazuli - meanders lazily around a plain of orchards and wheat fields. As you wander past, scenes from a Moghul miniature take shape in the fields around you: men are bent double beneath stooks of corn, reaping with sickles; others carry bundles of juniper branches for feeding to their goats.

The tarmac road had given up far below, and a shepherd boy had offered to lead me to my destination. We climbed up past mud-brick farms and through unharvested fields. Behind us the dying sun was sketching deep-cut shadows in the hills and I heard the distant ringing of bells as the shepherds led their fat-tailed sheep home for the night. We climbed on; and eventually, doubling back up the hill, we arrived.

It was an extraordinary sight. Perfectly preserved in the middle of nowhere lay a sophisticated and beautifully constructed monastic complex. It was built in a style that would not have been out of place in Rome or Athens: the ruins had porticoed and pedimented fronts, and were supported by carved Corinthian pillars. Halls, chapels, burial mounds - all were built in a style immediately recognisable as classical Greek; yet these were Buddhist buildings, a few miles from the Afghan border, and they dated from the early seventh century, long after the demise of classical civilisation in Western Europe.

I stood on top of the highest stupa. A crescent moon had just risen and though it was not yet dark, the cicadas were already whirring. Pillars of dung-smoke rose from the valley villages. I looked out over the Asian landscape, astonished by the classical vision in front of me. It was only much later, in the libraries back home, that I was able to make sense of what I had seen.

It seems that the origins of these strange buildings date back to the autumn of 327BC when Alexander the Great swept into these Highlands of Swat at the head of his victorious Macedonian army. Intending to conquer even the most distant provinces of the ancient Persian empire, Alexander had crossed into the Hindu Kush; and there, high on the Afghan plateau, he had first heard stories of the legendary riches of the Indian subcontinent - of its gold, said to be dug up by gigantic ants and guarded by griffins; of its men who lived for 200 years, and its women who made love in public; of the Sciapods, a people who liked to recline in the shade cast by their one enormous foot; of the perfumes and silks (which, the Afghans told the Greeks, grew on the trees and even in the cabbage-patches of India); of the unicorns and the pygmies, of the precious jewels which lay scattered all over the ground just like dust, and the variety of steel which could avert a storm.

But after Alexander's untimely death - in Nebuchadnezzar's empty palace in Babylon - the Greek garrisons of India and Afghanistan found themselves cut off from their homeland. They had no choice but to stay on in Asia, intermingling with the local peoples, and leavening the wisdom of India with Greek philosophy and classical ideas. Over the following 1,000 years, an astounding civilisation grew up in the isolated and mountainous kingdom. It was known as Gandhara.

Buddhist in religion - though worshipping an encyclopedic pantheon of Greek, Roman, Iranian, Hindu and Buddhist deities - Gandhara's principal icon was a meditating Buddha dressed in a Greek vestment. It is an extraordinary moment in world civilisation: the Hellenic roots of Western civilisation fused with the Buddha, the ultimate symbol of all that might be thought to differentiate the mind of Asia from the mind of Europe - and all this, one-and-a-half millennia before Kipling began holding forth on the impossibility of ever reconciling East and West.

Gandhara survived for 1,000 years, and when it finally collapsed it left behind in the hills of the North-West Frontier a legacy of finely constructed Indo-Hellenic monasteries (around Peshawar, a fifth-century Chinese traveller counted no less than 2,400 such communities) and also a scattering of classical cities and acropoli. There was also a wealth of Gandharan sculpture, most of which illustrates the Buddhist scriptures, but using the motifs and techniques of classical Roman art with its vine scrolls and cherubs, Tritons and centaurs. The slowly decaying remains of the culture which emerged from this extraordinary clash of civilisations still litters much of Northern Pakistan.

I had left Peshawar early in the morning the day before, and hitched out of town on a succession of brightly painted trucks. It was shortly before noon that I found my way to the ruins of Pushkalavati, the City of the Lotus.

Once upon a time, Pushkalavati had been a rival of the great Babylon, but its conquest by Alexander began a decline from which it never recovered. Today it is a strange and desolate ruin, more like a desert ziggurat than the ruins of the onetime capital of the fertile Punjab. The barren grey clay walls rise 80ft out of the cane-breaks, huge and sheer and craggy. Their original shape has been washed away by 3,000 years of rain. All that remains now is a Herculean block of mud, a series of local legends of a City made of Gold, and a lingering impression of strength and antiquity.

I climbed to the top of ramparts, unrolled a rug and sat munching away at my packed lunch; while I ate I listened to a shepherd boy playing a reed flute in the cane-breaks below. Afterwards I picked around the ramparts, trawling through the mass of pottery, bones and arrowheads which lay scattered across the hillocks of the ruin.

Handles of ancient amphorae, painted shards and fragments of geometric decoration lay strewn around like autumn leaves. At its height, traders came to Pushkalavati from all over the world: archaeologists have found alabaster from Rome, painted glass from Antioch and Alexandria, porphyry from Upper Egypt and lacquers from the China coast. Now it was just the shards and the mud and the ruins and me. I finished my lunch, pocketed a couple of glazed pot handles, and returned to the road.

The other great city of Gandhara lies south-east of Pushkalavati, at Taxila. When Alexander first appeared in the area, the king of Taxila wisely decided against challenging the Greeks. Instead he met Alexander in the Highlands of Swat and guided him through the forests of rhododendron and alpine clematis to the walls of the city. Here, for the first time, Alexander's troops were able to rest and take in the Indian scene.

To the Greeks, familiar with the glories of Athens, Babylon, Susa and Egyptian Memphis, the buildings of Taxila were unremarkable: the houses were made of mud and uncut stone, and were laid out without any central order or plan. But what did amaze the Greeks were the Pathans who lived there:

"Physically, the Indians are slim," wrote Alexander's Admiral Nearchus. "They are tall and much lighter in weight than other men... they wear earrings of ivory (at least the rich do), and they dye their beards, some of the very whitest of white, others dark blue, red or

purple or even green... they wear a tunic and throw an outer mantle around their shoulders: another is wound round their head..."

Others wore no clothes at all. Two miles outside Taxila, the Greeks came across 15 naked wise men who laughed at the Greeks in their cloaks and knee-length boots. They demanded that the foreigners should undress if they wanted to hear some words of the ancient wisdom of India. "But the heat of the sun," wrote one of Alexander's men, "was so scorching that nobody could have dared to walk barefoot, especially at midday." So the Greeks kept their clothes on, and the seniormost sadhu questioned them about Socrates, Pythagoras and Diogenes.

Although Alexander only stayed at Taxila for a matter of weeks, his visit changed the course of the city's history. Visiting the museum at the site, I wandered through the rooms looking at the Gandharan sculpture, some of which dated from nearly 1,000 years after Alexander's death. Even the Buddha, that symbol of Eastern philosophy, had undergone a process of Hellenisation: his grace and easy sensuality was thoroughly Indian; yet the images in the Taxila museum were all defined by Western ideas of proportion and anatomical realism; moreover he was wearing Greek drapery.

Most remarkable of all was the coin room. Over one entire wall were scattered the gold and silver coins of a millennium of Taxila's rulers. It wasn't just that the coins were all modelled on Greek originals. What was amazing were the names of the rulers: Pantaleon, King of North India; Diomedes of the Punjab; Menander of Kabul; Heliochles, King of Balkh. The coins hinted at the strange hybrid world these kings inhabited. They brought East and West together at a time when the British, the only other Europeans who succeeded in ruling the area, were still running through prehistoric fogs in bearskins. The coins of Heliochles of Balkh were typical: they showed a profile on one side - large nose, imperial arrogance in the eyes - but on the reverse Heliochles chose as his symbol a humped Indian Brahmini bull.

Remarkable as these remains are, it is difficult at first to understand how the warlike Pathans of the North-West Frontier could be descended from the gentle Greek philosophers who created the notably peaceful civilisation of Buddhist Gandhara. Yet they are, and if you look closely at the sculptures in the museum you can slowly begin to understand the connection which links the warlike tribesmen in the region's bazaar with the philosopher- soldiers of Alexander's army.

The most obvious link is material. In the wonderful friezes which illustrate the ancient Buddhist scripture, the Gandharan sculptors included details from everyday life, details which one can still see repeated in the lives of the people of the Frontier today. The writing-tablet and reed pen which the Buddha uses as a child can still be seen in primary schools. The turbans which the Gandharan chieftains sported in the sixth century AD have yet to disappear and many tribesmen still dye their beards, just as they did when Nearchus wandered through Taxila in the third century BC. The sandals of the Bodhisattvas are still worn; their musical instruments still played; their jewellery manufactured in the silver bazaar today. Even the design of the houses remains more or less unchanged.

But the link with the world of Gandhara runs even deeper than this. The Taxila museum is home to one of the most magnificent collection of Buddha images in existence. Room after room is filled with spectacular black- schist figures, standing, meditating, preaching or fasting. The images follow a prescribed formula. The physique is magnificent: muscles ripple beneath diaphanous folds. The saviour sits with half-closed eyes and legs folded, his hair oiled into a beehive topknot. His high, unfurrowed forehead is punctuated with a round caste mark. His face is full, his lips firm and proud.

It is only when you have stared at the figures for several minutes that you realise what is so surprising about the Gandharan version of the Buddha: it is its arrogance. There is a hint of self-satisfaction in the achievement of nirvana; a sneer on the threshold of enlightenment. This is the Buddha as he was in life - a prince. And soon you realise where you have seen that haughty expression before - outside in the bazaar. For unlike some of the other peoples of the subcontinent, the Pathans meet your gaze. Hawk- eyed and eagle-beaked, they are a proud people; and as the Buddhas demonstrate, their self-confidence directly reflects that of the Gandharan Bactrian Greeks who sculpted these images in the plains of Peshawar nearly two millennia ago.

Outside among the ruins, it is this strange mix of Europe and Asia that continues to grip the imagination. At Sirkap on the edge of Taxila, the Bactrian Greeks, descendants of Alexander's soldiers, founded a classical Greek suburb in 190BC. It was to be the New Taxila and they carefully laid out the different streets in a grid. As at Athens, a boundary wall loops around the residential areas and rises up to the citadel, Sirkap's Parthenon.

From there you can stand on the citadel walls and see the expanse of houses unfold beneath you. It is a scene of striking - almost suburban - regularity: it could be any modern New Town, except that each street is punctuated with Buddhist shrines, not supermarkets, and that the whole city was built nearly 200 years before the birth of Christ.

On my last evening in Gandhara, I went to my favourite Taxila ruin, the monastery of Julian, named after its founder, an Imperial Roman envoy who converted to Buddhism.

The monastery was always a place of retreat, and today it still retains its original calm. I arrived there late in the evening. It was that moment which Indians call Go dhuli bhela - Cow Dust Time - when in winter the smoke from the village fires begins to form a perfect horizontal line above the fields. At the foot of the hill, below the olive groves, leathery black water buffaloes sat with their legs folded up beneath them. Above, there were parakeets among the olives and, as you walked up the hill, flights of grasshoppers exploded from beneath your feet. Nearby lay a small shrine on which was inscribed the insignia of the double-headed eagle: centuries later the same symbol was to become the crest first of Byzantium, then of the Hapsburgs, and finally of Imperial Russia.

As I stared into the dusk, one question was still preying on my mind. How could it possibly be - in this multicultural age of ours - that the civilisation of Gandhara was so little known, and the implications of its existence so little appreciated?

William Dalrymple was a guest of Western & Oriental Travel (0171-221 8677). His book `The Age of Kali - Indian Travels and Encounters' is published by Flamingo (pounds 8.99)