I was deep in the Sahara, looking for a lost world. I only had a week and limited experience of finding lost worlds – but there was promise in the air. I was on the great caravan route that runs from the North African coast to Timbuktu. I had set off from Sebha, in southern Libya, in a Land Rover, with 150 litres of petrol, a sackful of cucumbers, quite a few tubes of lip salve, and the idea that the desert offered some kind of purity, a clean, exhilarating antidote to confusion and compromise.

My two companions were an Arab from the coast and a Tuareg from the desert. They were the original odd couple. The forefathers of the Tuareg had controlled the caravan routes of the Sahara, while the ancestors of the Arab had waited anxiously on the coast for their cut.

The Tuareg was a swashbuckler, the Arab a worrier. The Tuareg was tall and elegant, purple-black and swathed in an elaborate turban. The Arab was a short man in a baseball cap. The Tuareg was my driver, part of that freewheeling desert fraternity, men who were strangers to the Highway Code. The Arab was my translator. He had a jaundiced complexion and a knitted brow that the vast reaches of the Sahara did nothing to soothe. The desert was not really his kind of thing. He fretted over maps while the Tuareg regaled us with stories about lost expeditions.

I had begun my Libyan odyssey on the coast, at the Roman ruins of Sabratha and Leptis Magna. One of the finest cities of the Roman world, Leptis was once home to the emperor Septimus Severus. Had Septimus not died in Britain, trying to control barbarians in Yorkshire – always a hopeless task – he may well have succeeded in making Leptis the rival of Rome.

In ruin it is unrivalled. Paved streets lead through triumphal archways to the forum, to a colossal basilica, to a magnificent theatre overlooking the sea, to a vast and glamorous bathhouse built by Hadrian. There is even a Roman bar – the Laurel Wreath and Anchor, perhaps – that had once served a very decent palm wine. The secret of Leptis’s splendid ruin is that, unlike Rome, it was undisturbed by later building and was protected for centuries beneath sand. It is one of the great sites of the Mediterranean, whose blue waters curl at its feet.

But the point of Libya is not the classical remains of the Mediterranean world. The point is the desert. It is the desert that entrances, mystifies, confuses, thrills.

To readers of Paul Bowles, the trajectory of the journey into the desert is a familiar one. It begins with innocent curiosity on the coast and ends with disorientation, delirium and Debra Winger locked up in a harem in some remote oasis. In the desert there is the sense that anything might happen, and some of it will.

Things happening is what concerned the Arab. He had the air of a man on dangerously shifting sands. Ensconced in the back seat of the 4WD, gazing out at an empty nothingness, his features had settled into a rictus grin.

All day we drove south and west down the length of the Wadi al-Hayat, whose palm groves and barley fields were once home to the great Garamantes empire, the desert traders who were historic rivals of the Romans in North Africa. Ahead, the spectacular silhouette of Kaf Ejoul loomed close to the road. With its rock towers and domes, the mountain looked like a vast ruined fortress.

“Djinns or devil spirits gather on the summit,” the driver explained casually. “At night you could hear their drums beating, and see their fires.” The Arab pursed his lips and exchanged a meaningful look with me.

The Sahara has always appealed to people who see things that are not there. Misguided explorers, hopeless romantics, deluded legionaries, quacks, misfits, visionaries, obsessives, the deceivers and the deceived, they love all that emptiness. With a camel and a decent map of wells, any self-deluding fool can project his fantasies on that great Sabratha blank heart.

We spent the night at Ghat. I wandered through the old medina, now a ghost town of cool, meandering lanes. It took centuries to develop the delightful courtyard houses that allow people to survive in a hot climate. It took a few years to persuade the inhabitants of the medina, in the 1980s, to move to cement boxes in shadeless streets where they survive only with the benefit of air conditioning.

When I returned from the medina, I found the Tuareg in a quiet corner of a teahouse garden with a young woman whom he introduced as his niece. She seemed an admirably affectionate sort of niece. Meanwhile, round at the telephone exchange, the Arab was trying to get through to his wife back in Tripoli. She didn’t seem to be taking his calls. She was a good deal younger than him, and apparently the cause of considerable anxiety.

The next morning we abandoned the paved road for desert tracks. We were heading into the Jebel Acacus, a remote mountainous region hard by the borders with Algeria and Niger. The landscape was vast, its surface like the hide of some great prehistoric beast – tough, desiccated, scaly, with the bones of sharp rocks protruding.

But as we neared the Jebel Acacus, sand began to soften the surfaces. Dunes marched into the mountains, colonising whole valleys, their virginal slopes sculpted by the wind into sensuous forms. The mountains rose from these billowing sands like dark stalagmites. We wound from valley to valley in a rock-and-sand labyrinth until the Tuareg suddenly stopped at a tall cliff face.

Wadi Tashwinat, the Tuareg said. We followed him on foot up a track to a deep crevice at the base of the mountain. On either side, ochre-coloured figures swarmed across the rock faces. The painted scenes seemed anecdotal and unconnected. Groups of men charge at one another with bows and spears. Two women are dressing one another’s hair. Two men, chiefs perhaps, sit opposite one another, exchanging gifts. A giraffe lopes past in the middle distance.

Further on, above a sheltered ledge littered with sheep droppings, were scenes of hunters and of longhorned cattle. At the far end of the ledge, figures danced across the rock faces. A wedding, the Tuareg mused, picking his teeth with a thorn. At another site, a baby elephant trotted after its mother. Round the corner, beneath a vast rock face, were more giraffes, their legs askew, as well as camels and running stags. The paintings were delicate, elegant, almost ethereal.

They revealed a lost world. Millenniums ago, the Sahara was a rich savannah, not unlike the grasslands of East Africa, supporting large numbers of grazing animals as well as hunters and farmers. For the Sahara, climate warming began about 2,500BC, as cycles of drought and overgrazing stripped the land of its vegetation. The rock art of Jebel Acacus, with its animals and dancing figures, is a haunting echo of this vanished Saharan world. Dating, it is said, from as early as 10,000BC, they are some of the earliest “voices” on earth.

We drove on, rising over sand ridges to drop into another amphitheatre of craggy summits. And then another, and then another. The Arab and I were completely lost. Without any sign of human habitation, the valleys were a disorientating maze. Were we travelling deeper in the mountains or nearing their edge? Was this the valley, with its baroque rock formations, that we had passed through in the morning? Was that the peak we had seen from another angle? The late sun raked down the valleys, between elongated shadows.

When the Arab asked about a camp site, the Tuareg replied with an elegant, if noncommittal, wave of the hand. Among these bewildering valleys, he had a destination. In the last hour of daylight, as the sands turned the colour of almonds, we arrived at a small natural amphitheatre, enclosed on three sides by rock summits. Here, on a plateau of sand at the foot of the rock faces, we camped. Beneath us stretched a long valley, desolate and beautiful.

Night came with equatorial suddenness. One moment the sun was setting, the next the sky was packed with stars. A warm wind blew, a caressing easterly, coming from the Nile, a thousand miles away. After dinner I lay on the sand and counted constellations.

Then I sat up and gazed out towards the empty valley. In the desert at night you see things. Vague shapes seem to shift in that deceiving darkness. I thought I saw lights glimmering for an instant – out there where there was nothing – and then disappear.

I returned to the fire where the Tuareg was sitting crosslegged on the sand, making the tea. It is one of the great ceremonies of the Sahara, a complex alchemy involving endless pouring from one small pot to another. The Arab sat hunched on a camp chair rolling cigarettes, a habit he had picked up in Bournemouth when he was a language student. I mentioned the illusion of movement and light.

The Arab looked up, and gazed out into the darkness, beyond the fire. “There is nobody here,” he said. His voice was a squeak. The Tuareg looked across the fire at us, smiling his devilishly charming smile. “There is always someone there,” he said. “There are djinns, there are the ghosts of the old people. You have seen their paintings.”

The Arab slept in the car with the doors locked, his torch clutched in his hand. The Tuareg slept by the dying fire in a bed roll. I slept in a tent. The wind came up at night, flapping the tent as if someone had grasped the tent poles and was shaking them violently.

In the desert, mirage takes many forms. You make of it what you will.

Stanley Stewart travelled as a guest of The Ultimate Travel Company

Travel details: The Ultimate Travel Company (020 7386 4646, www.ultimatetravelcompany.co.uk) offers a fully escorted 10-day private tour of Libya, including Tripoli, Leptis Magna, Sabratha, and five days camping in the desert to explore the Jebel Acacus and the magnificent Ubari Lakes, from £1,578pp, including British Airways flights from Heathrow to Tripoli, transfers, entrance fees, guide, and all meals on safari. Cox & Kings (020 7873 5000, www.coxandkings.co.uk) has nine-day group tours to the Jebel Acacus from £1,495pp. Or try Silk Road and Beyond (020 7371 3131, www.silkroadand beyond.co.uk).

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