For the first two days after we set out, Callahan’s three students were in extremely high spirits. They were all young, and it was their first time entering the true interior of the Sahara, curious about everything, at times imitating Hassan’s whistles to drive the camels, at times chasing one another alongside the caravan, even shouting from the tops of dunes and letting their voices scatter into the open emptiness. I felt restless as well; the scale of the desert creates a strange exhilaration, as if heaven and earth have been reduced to nothing but yourself, but since I was responsible for field coordination, I had to straighten my posture in the saddle, suppress the impulse, and wear the expression of someone who knows exactly where he is going.

  According to Hassan, this first stretch of travel did not yet count as real sand sea. The area around Siwa once received far more rainfall during the Holocene humid period, the underground aquifers have not completely dried, low depressions still show saline surfaces and traces of former wetlands, the sand layer is shallow, and pale sedimentary rock occasionally breaks through the surface, remnants left behind when ancient lakebeds evaporated. Along certain dune margins, calcium crust appears in fractured white lines, evidence that stable bodies of water once existed here.

  Moving in the direction of what we suspected to be an ancient river course, subtle differences in elevation could be detected, and in one zone the dunes curved in an unnatural linear arc, not shaped by wind direction but more like terrain carved over long periods by flowing water. Callahan marked the coordinates with a handheld GPS and said this might indicate the preserved direction of a prehistoric channel.

  Once we crossed the last remaining trace of that old riverbed, we truly entered the Great Sand Sea. The ancient watercourse had long vanished, leaving nothing but endless dunes stretching southwest, Gilf Kebir faint in the distance, and the region we were entering was what locals call the “Black Sand.” Hassan said the black sand is punishment for greedy men. “Many cities under sand, much money,” he said. “Man go in, take little, not come back. Road run away.” He spoke in a calm tone, as if discussing a stubborn camel.

  “City still under,” he said. “Water gone, people gone, city stay. Sand cover.”

  It sounded like legend, but Callahan added quietly that the Sahara was not always arid; after the humid period ended, large numbers of settlements were rapidly abandoned, and within a few centuries wind could completely bury surface architecture. This was a highly mobile sand sea, where wind could reshape the landscape overnight, dunes recognizable one day entirely altered the next, and the ancient river channel long erased; without Hassan, the half-buried stone walls, the tilted remains of mud structures, the wind-twisted dead trees, and the few scattered desert shrubs would have escaped us, yet he linked these fragments into an invisible line pointing toward where the river once passed, and at the end of that vanished watercourse lay the region where Zerzura might have existed.

  What impressed us most in the desert were the dead trees that had never fallen, trunks ground almost flat by wind-driven sand, branches twisted in the same direction like some frozen gesture, standing for centuries in a climate that should have erased them long ago. The first light of morning rose in the east, staining the clouds red, waves of dunes washed in gold, the dry tree shadows and rippled sand turning copper and crimson in the slanting light, the colors so heavy they felt almost unreal.

  To avoid the midday heat, we had marched through the night, and though exhausted, the sight revived us; Caroline murmured that the desert was more beautiful than she had imagined and raised her camera to take photographs. While everyone else was absorbed in the view, I noticed Hassan staring at the eastern sky, something uneasy in his expression. I walked over and asked whether the weather was about to turn. He nodded and remained silent for a moment.

  “Cloud bleeding,” he said. “Wind come. Inshallah.”

  He did not sound like he was praying; he sounded as if he were making an announcement. I joked that the wind would not hold a grudge against us. He frowned.

  “Cloud low,” he said. “Wind come fast. Sand run.”

  From a meteorological perspective, red morning clouds often mean dust has already formed bands at altitude, and once surface pressure shifts intensify, wind strengthens quickly. Hassan said the storm would be severe.

  “Do not joke,” he said. “Sand hear.”

  This was our fifth day out, and the third inside the black sand zone. Ahead lay the ruins of the western site, and we had originally expected to reach them the following day, but Hassan said the coming storm would be too strong, no sand wall would stop it, and unless we reached the stone remains near the ruins we would be buried in the desert. I knew he was not exaggerating; we still had more than half a day’s travel ahead, and we had marched through the entire night, the team worn down, and it was uncertain whether the students could hold up.

  I was about to urge everyone forward when Hassan slowly dismounted, spread a small mat on the sand, knelt, raised his hands to the sky, and recited quietly. This was his morning prayer, a ritual he never missed. I assumed the situation could not be that serious, otherwise he would not be so composed. But when he finished, he changed completely, rolled the mat in seconds, leapt back onto his camel, and let out a long piercing whistle.

  “Run, run! Late, sand bury!”

  He drove his camel forward at once. I cursed and signaled the others to move. The camels seemed to sense the danger in the air, bursting forward with all four legs, and though riding them at a slow sway can feel almost pleasant, once they break into a run the jolting becomes violent, and we flattened ourselves against the saddles, gripping tightly to avoid being thrown.

  The caravan raced across the sand sea, trailing a long plume of yellow dust, everyone wearing goggles and wrapping cloth over nose and mouth, and I kept counting heads left and right, feeling increasingly uneasy as the camels nearly lost control, following Hassan’s lead mount at a pace that felt driven by the wind itself. My greatest fear was that someone would be thrown; I tried to shout for him to slow down, but I could not open my mouth without swallowing sand. We ran until near noon, and even the camels showed signs of fatigue before finally slowing, fortunately with no one missing.

  Hassan told everyone to eat quickly and drink water without worrying about supply, saying groundwater could be found beneath the western ruins to replenish what we used, and once finished we must move again immediately or it would be too late. The team chewed dry rations in haste while Carter and I checked each member.

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  Callahan, the oldest among us, was shaken by the ride and barely able to speak, the youngest female student pale and able only to sip water. The most troublesome case was Daniel, who had lost his spare goggles and could see almost nothing until another student lent him backup lenses of nearly the same prescription. Caroline and the tall student beside her were holding up well, especially Caroline, who perhaps inherited her father’s temperament, remaining steady after a sleepless night and a half day of running across the sand, even helping Hassan secure the loads on the camels. A thin wind swept across the dunes, lifting fine sand, and the distant horizon gradually turned dark yellow.

  Hassan shouted, “Wind come! No stop!” The team mounted again, no longer conserving the camels’ strength. The sky darkened rapidly, the wind rose hard, sand lifted into the air, visibility dropped, and in the confusion I counted again. Including myself, there were eight.

  One was missing.

  The wind grew fiercer, sand sweeping across everything, until the world was reduced to a dull yellow haze, and I couldn’t tell who had fallen behind, but the caravan had only just come down the dune, maybe a hundred yards, and if I turned back now, I could still reach them. The first person I thought of was Caroline; if something happened to her, the expedition would be over, but the thought passed in an instant and I forced it down, a life is a life, sponsor or student, no one gets left in the sand.

  Carter was beside me, the only person I could still make out, I tried to speak to him, but the wind was too strong and I couldn’t open my mouth, so I gestured wildly from the saddle, signaling him to stop Hassan, who was driving the camels hardest at the front. In that brief delay the twenty camels surged another several dozen yards, and without waiting to see whether Carter understood, I swung off the running camel and hit the ground.

  The hoofprints were already being erased by the wind and would soon disappear entirely, I ran back against the gale, my body like a sheet of paper caught in the air, each step unsteady, hearing nothing but the roar of sand. After nearly two hundred meters, on the ridge where we had just rested, I saw someone lying on the ground. The figure was half buried, unmoving, and I rushed forward and dragged him out of the sand.

  It was Professor Callahan.

  He had already been struggling, and in the chaos he must have been thrown from his camel. Callahan was alive, only stunned, unable to speak, and when he saw me he reacted with sudden emotion and then lost consciousness. The wind was strong, but I knew this was only the beginning, the real black wall of sand could descend at any moment, and there was no time to waste. I hoisted him onto my back, glanced behind me, my own footprints still barely visible, and prayed Carter had managed to stop Hassan, who had been charging ahead without looking back. I tried to carry Callahan down the slope, but the wind from behind was so violent that I couldn’t keep my footing, and we both tumbled down the dune, and through the yellow haze someone pulled me upright.

  It was Carter.

  He had understood, striking his camel hard and pushing forward to tackle Hassan straight off the lead saddle, and when the lead camel stopped the rest of the herd halted as well, except for one panicked animal that bolted forward and vanished into the curtain of sand. Luckily they had not gone far, otherwise we never would have regrouped. No one could speak, we communicated only by hand signals, understand if you can, copy if you can’t, and we prepared to remount. But the camels seemed terrified, refusing to move no matter how they were struck, kneeling in a row with their heads buried in the sand.

  We had seen camel skeletons like that along the way, preserved in the same posture, as if they had chosen to kneel. Hassan said they did this when the black wind came, they knew the storm was coming and that running was useless, so they lay down instead. We stood there helpless, were we really going to wait to be buried alive? Just then Caroline grabbed my arm and pointed west, signaling us to look. Through the storm a massive white shape was charging toward us, already close, but the wind drowned out all sound, and instinctively I pulled the short rifle from its scabbard by the saddle, our perimeter security weapon, and everyone focused on the shape, it wasn’t a man.

  The white figure reached us in an instant, a large single-humped camel, completely white, its coat bright against the yellow storm, its neck lowered into the wind as if it knew exactly how to cut through the sand.

  “White camel,” I heard Hassan mutter.

  Even through my goggles I could see the light in his eyes, not wonder, but recognition, the look of someone who had just found a way out, and he lifted his arms and shouted praise to God into the storm, and the kneeling camels slowly raised their heads. I did not understand what was happening, but instinct told me this was our chance, follow the white camel, it belonged to this sea of sand and understood wind and terrain better than we ever could, and I signaled the others to mount and move after it.

  The white camel turned without hesitation, running along a lower sand ridge, and the herd followed as if pulled by a rope, the camels foaming at the mouth as they pushed the last of their strength, tightly following the white figure, cresting a massive dune where the terrain suddenly rose, and then the white camel flashed once and disappeared.

  My stomach dropped.

  Before we could understand what had happened, our mounts turned on their own and circled the high ridge, and along one flank of the dune a broken stretch of wall emerged, with a compacted earthen structure beneath it. It was the ruins of an ancient settlement. Most of the structures were half buried, some had collapsed, and only a section of heavy wall still stood above the sand, weathered into the same color as the desert, so that from a distance it would appear to be nothing more than a sand formation, and without approaching from the side one would never discover it. The white camel had run into the shelter of the ruins, disappearing behind the broken walls. The wall stood like a natural windbreak, whether it could withstand the coming storm, as Hassan said, was “for God to decide,” but in such circumstances any cover was mercy.

  We dismounted, faces yellow with sand and fear. Hassan forced the camels to kneel tight against the wall, turning their heads toward the leeward side, and then led us through a collapsed roof opening. Though the city walls offered some protection, years of erosion had allowed sand to pour steadily inside, and the floor was layered with fine dust nearly two meters deep. The hall we entered was large, like some administrative building or storage chamber, yet even so we had to stoop as we moved, and lifting one’s head slightly would mean striking a beam.

  Emily and Mark, already exhausted, collapsed onto the sand and gulped water. We carried Callahan inside, he was conscious now but his legs trembled, and Carter let out a long breath and said we had bought our lives back. Hassan knelt again in the sand, raising his hands, pressing his forehead to the ground, reciting prayers in thanks for the white camel that had delivered us from the storm, saying that such animals were blessed and not everyone was meant to see one.

  “If there is someone God does not favor,” he said, “we would not see it. The wind would take us all.”

  I cursed under my breath, remembering how fast he had driven the herd before.

  Outside the full force of the storm struck, the wind howled and shook the walls, and we worried the entrance might be sealed. I assigned Carter, Mark, and David to watch the opening in shifts, ready to evacuate if it began to fill, though we all knew that if the outer wall disappeared, running would only mean dying somewhere else. Dry desert brush grew at the base of the wall, I gathered some and lit a small fire with solid fuel, and the flames pushed back the darkness of the ancient hall.

  Suddenly Emily sprang up and struck her head against a beam, sand showered down, and everyone rubbed their eyes. They asked her what was wrong, and though my own vision was blurred with grit, I heard her trembling voice.

  “In the right corner… there’s a body.”