I STAYED ON in El Oued, and in the early hours walked south along a crumbling paved road under assault from the sand sea. The morning was bright and hot, and the dunes carved crisp lines against the sky. I passed a turbaned man on a donkey carrying empty gas cans into town. There was no other traffic. The minarets of El Oued disappeared behind me. The road led eventually to a village, or what was left of it. It was a village that had been mostly buried in drifting sand. The corners and roofs of stone structures still showed, but only three houses remained inhabitable, and from the evidence of digging around them, they, too, were threatened.

I drank at a well with a rope and bucket. There was no farming here. The only sign of industry was a freestanding stone oven, a baker's oven, against which palm wood had been stacked. The wind blew sand, but otherwise nothing stirred. Two men sat in the shadow of a wall by a fire on which they had placed a blackened pot. They motioned me over and offered me tea in a dirty glass. The men were older than I, bearded and thin, and had no work. We spent a few hours together. They pointed to where the school lay buried, and to where most of the village stood beneath the sands. I asked them the details of its burial.

They said the sands are fickle. Dunes may drift for decades in one direction, or not drift at all, then suddenly turn and consume you. Consumption by the sand is like other forms of terminal illness: it starts so gently that at first you don't worry. One day the grains begin to accumulate against your walls. You've seen the grains before, and naturally assume that a change in the wind will carry them away. But this time the wind does not change, and the illness persists. Over weeks or longer, the sand grows. You fight back with a shovel, and manage to keep your walls clear. Fighting back feels good and gives you something to do. But the grains never let up, and one morning while shoveling you realize that the dunes have moved closer. You enlist your sons and brothers. But eventually the land around your house swells with sand, and you begin standing on sand to shovel sand. Finally no amount of digging will clear your walls. The dunes tower above you, and send sand sheets cascading down their advancing slip faces. You have to gather your belongings and flee.

But your house is your heritage, and you would like somehow to preserve it. As the dunes bear down on it they will collapse the walls. The defense is again the Saharan acceptance of destiny: having lost the fight against the sand, you must now invite it in. Sleeping on the sand ,covering your floors with it for all these years, helped prepare you mentally. But shoveling in the sand is not enough. Your last act is to break out the windows, take off the doors, and knock holes in the roof. You allow the wind to work for you. If it succeeds, and fills your house, the walls will stand. Then in a hundred years, when the wind requires it, the dunes will drift on and uncover the village. Your descendants will bless God and his Prophet. They will not care that you were thin and poor and had no work. They will remember you as a man at peace with his world. The desert takes away but also delivers.

I LEFT THE men to their contemplation, and climbed out over the dune that had engulfed their village. From its crest I discovered a valley two hundred feet below, where the desert floor was exposed and a stretch of blacktop emerged from the sand. The road was not on the map. It lay beyond the village and ran south toward the empty center of the Eastern Erg. I thought it might lead to an old settlement, perhaps one that had been uncovered by the wind, and I set off to follow it.

I should have been more careful. I was traveling too lightly, with neither a hat nor water nor any enduring sense of direction. The road kept turning, diving into sand, reemerging. Eventually it ran under a mountainous dune and disappeared entirely. I climbed that dune, and a string of the highest ones beyond it, and knew even as I proceeded that I had gone too far. The dunes were like giant starfish, covered by ripples, linking curved tentacles to form lines. In all directions, the erg stretched to the horizons in a confusion of sand.

This was the landscape that inspired the British officer Ralph A. Bagnold, history's closest observer of Saharan sands. Bagnold was an English gentleman of the old school. He fought in the trenches of Flanders during World War I, then earned an honors degree in engineering from Cambridge, and later reenlisted in the British Army for overseas assignment. While stationed in Egypt and India between 1929 and 1934, he led expeditions in modified Fords to explore the sand seas of Libya. These were big places in need of understanding. One erg alone was the size of all France.

Bagnold had a strong and inquiring mind. He marveled at the desert's patterns, saw magic in the dunes, and wanted it all explained. To his surprise, he found that scientific knowledge was as yet merely descriptive: dune shapes had been catalogued, but little was understood about the processes involved in their formation. Bagnold set out to understand for himself. In 1935 he went back to England, retired from the army, hammered together a personal wind tunnel, and began a series of meticulous experiments with blown sand. He considered himself to be a dabbler, a tinkerer, an amateur scientist. But his research resulted in the publication, in 1941, of a small masterpiece of scientific exploration: The Physics of Blown Sand and Desert Dunes. It was a treatment so rigorous, and so pleasantly written, that it remains the standard today. Throughout it, Bagnold never lost his wonder. He wrote:

Here, instead of finding chaos and disorder, the observer never fails to be amazed at a simplicity of form, an exactitude of repetition and a geometric order unknown in nature on a scale larger than that of crystalline structure. In places vast accumulations of sand weighing millions of tons move inexorably, in regular formation, over the surface of the country, growing, retaining their shape, even breeding, in a manner which, by its grotesque imitation of life, is vaguely disturbing to the imaginative mind.

Bagnold's genius was his ability to think grain by grain. He defined sand as a rock particle small enough to be moved by the wind, yet not so small that, like dust, it can float indefinitely in suspension -- and he proceeded from there, exploring the movement of each grain, He did his best work on that level, in a laboratory far from the desert. But he was never a tedious man. He understood the power of multiplication. And when he returned to the Sahara, and stood as I did on the crests of the great ergs, he found in these accumulations his truest companions. Just before his death, in May 1990, he wrote a short memoir -- an unintentionally sad remembrance of a strong life. He wrote about two world wars, about great men he had known, and about his beloved family. But again he wrote best about the sand. Bagnold's health was declining. It is a measure of the man that when he described the dunes' ability to heal themselves, his writing remained free of longing.

I GAVE UP on finding the road. For all I knew it ended where I stood, in a lost village hundreds of feet below. My tracks led back toward El Oued in the thinnest trace, softening already in the wind. The sand was a brilliant shade of tan that reflected the sun and filled the air with its heat. Bare rock can produce the same effect. As a result, the Sahara is one of the most reflective places on earth: in heat and light, it fends off 90 percent of the solar energy that assaults its surface. For burrowing creatures like scorpions, this has an essential side effect -- it means that just inches underground life feels cool. For creatures above the surface, however, all that redirected energy poses problems. This is something Bagnold hardly bothered to mention: by early that afternoon, when you walk across the sands, the sun burns you from below.

Though I happened to carry a small thermometer, I did not measure the temperature on the Eastern Erg. It was autumn, a gentle season, and I had already been through the greater heat of Saharan summers. Still my hands trembled, and I suffered from the dryness of mouth and tightening of the throat that marks the onset of deep thirst. Retracing my path across the sandy swells, I thought wishfully about more genuine seas.

Imagining water is a normal human reaction to the Sahara. For that reason, and because of the superficial resemblance of the ergs to stormy seas, comparisons to the ocean are inevitable. Still, they have been overdone. Camels are not ships, and nomads do not sail across the sand. Erg is Arabic not literally for a sea but for a vein or belt. Dunes do undulate, but they never form genuine waves. Bagnold wrote:

The resemblance [to a wave] is in appearance only. For the essence of a true wave is the propagation of energy, either through the body of a material as in the case of sound, or along its surface as with a surface water wave. In a sand ripple or wave there is no such propagation of energy. A sand ripple is merely a crumpling or heaping up of the surface, brought about by wind action, and cannot be regarded as a true wave in a strict dynamical sense. The similarity lies only in the regular repetition of surface form.

On the subject of sand, Bagnold was disciplined. He distinguished sternly between drifts, which form below windbreaks, and "true dunes," which achieve their greatest perfection on flat, featureless ground. True dunes breed incestuously, and live in immense look-alike families, sometimes extending across hundreds of miles. Their features depend on the wealth of the sand supply, and on the force and direction of the prevailing winds. In detail they seem infinitely variable. However, it is possible to distinguish between a few basic types.

The barchan is the elemental one -- a migratory, crescent shaped formation with a gentle windward slope up which grains slowly creep, and a steep leeward slip face down which those same grains eventually cascade. Barchans advance by avalanche, sending shallow horns ahead on each side. They are solitary by nature, and careful conservationists: born of unidirectional winds and limited resources, they retain their shape and bulk by constantly turning over their supply of sand.

Where sand supplies are abundant, the barchans multiply in ever-denser colonies, until eventually they link horns to form scalloped chains perpendicular to the wind.

As the sand thickens, the chains become high ridges across which smaller secondary barchans may begin to migrate. Such compound crescent-shaped dunes are common to the northeast corner of the Eastern Erg, and to other parts of the Sahara where the wind blows from a single direction.

Where the wind is fickle, the sand assumes an entirely different form. Bidirectional winds herd the grains by pushing first from one angle, then shifting and pushing them from a slightly different angle, finally organizing them into elongated formations that stream downwind in parallel ranks.

Bagnold described these dunes with the word sief which is Arabic for "sword." But they are more like serpents in the way they hump and crawl across the desert floor.

Where the winds blow energetically from around the compass, typically in a pattern of regular seasonal shifts, the sand crawls around less, but builds upward into high-peaked imitations of starfish.

Star dunes embrace El Oued with their tentacles. When one of them stretches, whole villages may disappear.

The forms that dunes take in real sand seas are rarely as simple as their idealized models. Even the concept of sorting -- by which the dune types are meant to keep mostly to themselves -- is more useful as a theoretical tool than as a practical guide to the field. Bagnold's first achievement, without an airplane and in a time before satellite mapping, was to visualize the geometry. Star dunes sprout on the crests of crescents, which bleed into barchan-crossing barchans. Bagnold's "simplicity of form," his "exactitude of repetition," and his "geometric order," tangle together with the symmetry of a maze.

I blundered into that maze now. Having left my earlier tracks to skirt the highest peaks, I climbed a ridge to reconnoiter, and instead of spotting the old road where I had expected it, found only sand. I could have doubled back to my earlier tracks, but I felt sure the road lay nearby -- over the next ridge, or the one beyond. My thirst urged me ahead. I had a few hours still, because the season was not summer, so I was not immediately afraid. But I knew enough about the Sahara to want to keep moving. I ignored the romance of the erg and the mechanics of its dunes. I remembered the stories.

IN A NORTHERN oasis I once met an old drunk named Lag Lag, who as a young man had made his living driving cargo trucks across the roadless Sahara. We met one night by a campfire, to which our mutual friends had lured him with an offer of cheap wine. He was a wiry, good- humored old man with unkempt hair and ragged clothes. His friends told me he had been a pious Moslem in his younger years, but they warned me that his drinking had made a mockery of his faith. They thought his story needed to be told anyway, and they wanted me to write it down. Lag Lag was a famous man, not because twice he had been lost in the Eastern Erg but because twice he had survived.

He told me he was first lost in the summer of 1957, when he and an assistant were hauling equipment south from Biskra to the newly discovered oil site at Hassi Messaoud. Rather than driving their truck the long way around across the hard gravel plains to the west, they decided to cut straight through the sand sea. It was a bad idea. Driving among dunes is slow and frustrating work, and requires scouting for soft sand; it imposes frequent turns and backtracking, and soon confuses even the best sense of orientation.

Neither Lag Lag nor his assistant was a navigator. They knew only that the sun rose from Mecca, soared high all day, and plunged into the west, and that it was chased all night by a universe of stars. And so they began to wander. Eventually they realized that nothing looked right, but they did not panic. For three days they struggled with the dunes, until they ran out of fuel.

Since they carried water, they were in no immediate danger. But the long-term prospects were not good. Walking out was unthinkable, and it was unlikely that anyone would come their way. The oilmen at Hassi Messaoud expected them, of course, but had no idea of the route they had chosen. The possibility of aerial search did not enter their minds. It was accepted then as now that people die in the desert.

The sun forced them into the shade under the truck, where they dug a shallow trench. Day after day they lay there, watching their water dwindle and waiting for God's will. They turned inward to Islam and talked about the afterlife. They had food, but did not eat, fearing it would magnify their thirst. Dehydration, not starvation, is what kills wanderers in the desert. And thirst is the most terrible of all human sufferings.

The physiologists who specialize in thirst seem never to have experienced it. This surprises me. You would think that someone interested in thirst would want to stop drinking for a while, especially since for short periods it can be done safely. But the physiologists pursue knowledge, not experience. They use words based in Greek, which soften the subject. For instance, they would describe the Sahara -- the burning sand and relentless sky -- as dipsogenic, meaning "thirst provoking." In discussing Lag Lag's case, they might say he progressed from eudipsia, meaning "ordinary thirst,' through bouts of hyperdipsia, meaning "temporary intense thirst," to polydipsia, by which they mean "sustained, excessive thirst." We can define it more precisely: since poly means "many," polydipsia means the kind of thirst that drives you to drink anything. There are specialized terms for such behavior, including uriposia, "the drinking of urine," and hemoposia, "the drinking of blood." For word enthusiasts, this is heady stuff. Nonetheless, the lexicon has not kept up with technology. Blame the ancients for not driving cars. I have tried, and cannot coin a suitable word for "the drinking of rusty radiator water."

Radiator water is what Lag Lag and his assistant started into when their good drinking water was gone. They had been under the truck for three weeks, and no one had come to find them. They wrote good-bye letters to their families, and stuck them up in the cab.

The assistant sobbed.

Lag Lag was annoyed, and said, "When you die, you die." He lay quietly, preparing for the end.

Years later when he described his peace of mind to me, I admitted to him that I found it strange. Afterward, I would have my own experience with a stranding in the Sahara. But Lag Lag was the first to say to me that such a death is not complicated, that the Sahara overpowers its victims and offers no choice but acceptance, that Islam too requires acceptance, that the greatest God is the desert God.

They had drunk most of the radiator water before Lag Lag had his inspiration. It occurred to him that the truck's tanks might still hold dregs of diesel fuel, and that he might add engine oil to form a combustible mixture. Having passed from tears to hopelessness, his assistant refused to move from under the truck. Lag Lag ignored him, and drained as much oil as he dared from the engine before pouring it into the tank. He climbed into the cab, cycled the glow plug, and pressed the starter. The engine turned over reluctantly, but after several attempts rumbled to life. The assistant scrambled aboard. Spewing dense blue smoke, the truck rolled forward.

After a few miles they came to a rutted track. With no idea of where they were, or of where the track led, they followed it. Because they had drunk most of the coolant, the engine overheated and seized. But the desert spared them: a refrigerated van appeared in the distance, shimmering in the heat, and drove up the track to them, carrying water, fresh meat, and vegetables. It was driven by a friend. He broke the seal on the back, and built a fire. Lag Lag and his assistant drank and feasted. The specialists would say they rehydrated.

AFTER ALGERIA'S WAR of independence, Hassi Messaoud kept producing oil and gas for the new nation. Lag Lag kept driving the open desert, and allowed his memory of the sands to fade. He no longer willingly cut through the erg, but in 1964 he agreed to deliver a massive concrete cap to an oil site deep in the dunes. His youngest brother went with him. They drove to an oasis on an established track, then set out into the sand. By the end of the first day they were lost. They doubled back by scouting their tracks, which in places had already been obliterated by the winds. At night they slept. On the second day, through miscalculation, they allowed the truck to sink into soft sand.

Because sinking into sand is a routine part of driving the open Sahara, even outside the ergs, Lag Lag was not at first concerned. You shovel sand or dig it with bare hands from the dikes that build in front of the wheels, and drive on. In a bad case, getting unstuck might take a few hours. But this time the sand was different, so fine and soft that digging only caused the truck to sink farther in. They tried pushing the concrete cap off the truck, and when that didn't work they tried prying it off. The cap was too heavy; it was a weight dragging them to the bottom of the desert. By the end of the day, Lag Lag realized that again the erg had trapped him, and all his memories returned.

His brother volunteered to walk out. Lag Lag feared the futility of an attempt, and argued that if they rested in the shade of the truck and did not struggle they would have enough water for perhaps a week. If God intended it, someone would discover their tracks or happen along. If not, Lag Lag said, it would be better to meet death quietly, like men. When you die, you die.

The week passed, and they drank their last water. Lag Lag realized no help was coming. Only the radiator fluid remained. He felt proud of his brother, who prayed not for salvation but in acceptance of God's will. Lag Lag's own mood was fatalistic, but not to the point of inaction. He decided on the basis of his past experience that lie was destined to find a solution.

Lag Lag's solution was not original; he had never been much of a thinker. But his thirst forced him to concentrate. With his brother's help, he bled the tires, and bled them further until they bulged like pancakes in the sand. I know today how their work sounded then -- the sharp hiss of escaping air penetrating the desert of naturally broader winds. They waited for night, and dug sand ramps for the truck to climb. That work sounded like two desperate men breathing hard. Then they waited for light.

In the moments before dawn, when the horizon first promised the sun, they prayed. Lag Lag climbed into the cab. He started the engine, and as a diligent driver, let it warm. He shifted into compound low. His brother stood outside, adding one manpower to the strength of the diesel. Together, with the clutch sliding and burning, they drove the truck from the grave.

They were still in danger: they carried no pump to reinflate the tires, and the rubber would soon peel from the wheels. Their water was gone, and their tracks from the week before had disappeared. Flawless sand lay all around. They set off in what they hoped was the right direction. And fate was with them: after barely two miles, having crossed the tentacle of a star dune, they found below them the same little oasis from which they had started.

It was a quiet place with a mosque and a post office. The residents were unimpressed by the sight of two men emerging from the desert. A few might have noticed their beards, and the condition of their tires. Someone gave them water, someone sold them food. Lag Lag pondered the deeper meaning of their ordeal. They had lain nearly within shouting distance of the oasis, but as good Muslims they had not shouted. It was all quite mysterious to him, and only added to the glory of God and the desert. Years afterward, when I met him, the sadness of Lag Lag's later life was apparent to everyone at the campfire. Having exhausted an old story, he had nothing left to say. With time and wine, he had allowed the memory of his desert to soften.

MY OWN EXPERIENCE in the Eastern Erg was less threatening than his. I walked, grew thirsty, and imagined cool water. And where I thought I would find the abandoned road or the half-buried village, I found instead a farmer with a camel, tending his palms behind a palm- frond fence. He was dressed in pants and a shirt, and wore a loose turban. He seemed unsurprised that I had strolled out of the dunes.

"Bonjour monsieur," he said, in accented French. "You have enjoyed your walk?"

I said I had.

He offered me water, and I drank deeply. He watched this with interest. Saharans sip. He said, "We used to see a lot of Europeans here, just a few years ago, because we have the finest dunes in the entire Sahara. Did you know that Monod himself was here?" He meant Théodore Monod, the lyrical Jacques Cousteau of the desert. Among Saharan explorers I prefer Bagnold, whose austerity was truer to the desert itself.

I said, "I'm not French."

"I know. You're American."

"You can tell from the accent?"

"You came in the taxi from Biskra. My cousin rode with you."

I laughed. "What else do you know?"

"You don't like scorpions."

"That's easy."

"Last night you sat with the French couple at the hotel. They had scorpions in a box." He smiled. "I have a cousin at the hotel, too."

He felt like bragging. He said, "I also know that you posted a letter to the United States. The Parisians tried to telephone Paris, and couldn't get through. But you -- you did not even try the telephone."

Material reprinted with permission of the author and the author's agent, Darhansoff & Verrill Literary Agency, © William Langewiesche - All Rights Reserved. - William Langewiesche is a Contributing Editor of The Atlantic Monthly, where his writing on the Sahara first appeared. Sahara Unveiled is available in hardcover from Pantheon Books, a division of Random House, Inc., and can be ordered on-line through Amazon.com. - Quotations are from "The Physics of Blown Sand & Desert Dunes" by R.A. Bagnold (New York: William Morrow & Co., 1942) and were reprinted with permission of Chapman and Hall.

The rugs which illustrate this story were made by carpet makers from Afghanistan currently living in Pakistan. Rugs provided by Ann Benton - Carpet Photography © OneWorld Magazine - All Rights Reserved.