Erg Chebbi is a range of orange sand twenty-two kilometres long in southeastern Morocco, near the Algerian border, with dunes climbing 150 metres. The odd part is the ground it sits on: a flat stony plain with no other sand on it. Merzouga sits at its foot, and the camels line up at the edge of the village every afternoon. The ride out goes in single file, the old caravan way, once the heat has eased. You sway along with the ridgelines throwing long shadows over the sand until the camp appears in a hollow between the dunes. The camp is pitched the way desert travellers always pitched them: a shared tagine, drumming by the fire, and then a silence that feels physical. The climb starts in the dark. You go up the tallest dune above the camp, feet sinking into cool loose sand at every step, and from the crest the sun lifts over the Algerian border and sets the erg glowing. The same climb pays at dusk, when the iron in the sand runs gold, then rose, then deep copper-red.
By day the dunes are a playground: boards go down the steep leeward faces and 4x4s climb and drop over the ridges. From June to September the sand itself is the treatment. People are buried in it up to the neck for rheumatism and back pain, sweating within minutes, and anyone with heart trouble is turned away. The caravans that crossed here carried gold north out of West Africa and salt south to pay for it, as far as Timbuktu. Sijilmassa, founded in the eighth century near what is now Rissani, grew rich taxing it, and its mud-brick walls still stand north of the dunes. After a wet winter the shallow lake west of Merzouga fills and flamingos come to feed on its brine shrimp. In dry years the bed stays bare. And at the edge of the erg the sand simply stops. One stride takes you off it onto flat black stone running to the horizon, with the whole dune wall standing behind you.