The well-equipped come by light aircraft. The less so, or the more adventurous, approach the great wall of Algeria’s Tassili mountains by four-wheel-drive truck, crossing gravel, rock and shifting sand where the air shudders above a ground temperature that can reach 70°C (158°F).
Their destination is not a mountain range in the usual sense, though it rises to 7400ft (2250m) above sea level. Rather, it is a 400-mile (640km) long sandstone plateau, dissected into separate massifs which are themselves split and divided again by numberless ravines and wadis into a chaos of cliffs and pinnacles of naked rock. It is a place of strange beauty that has few equals.
Best, perhaps, to see it first at dawn, when its twisted buttresses are touched by fire, rose and purple, and throw indigo shadows across the intervening sand. Then, with only a touch of fancy, the eroded rock turns into skyscrapers and cathedrals, spires and chimneys.
Though the sand-laden wind was the artist that carved the softer rocks into shapes for the imagination to seize upon, the principal architect was water. Rushing torrents gouged out ravines, isolated bluffs from stacks and monoliths, split seams and fissures and excavated shallow caves.
The area is now known as the Sahara once had a wetter climate. Many of the dry, sand-filled wadis and ravines on the desert’s southern margin were then rivers or occupied by Lakes. What is now desert was once green grassland.
Drying was a slow, slow process; the very name Tassili N’Ajjer translates as ‘Plateau of the rivers’, though it has been arid since long before the beginning of the Christian era.
Staunchly surviving from this wetter time are small groups of gnarled cypress trees whose roots burrow into the rocks in search of water. They are reckoned to be 3000 years old and are the last of their line, for although they produce viable seed, the ground is too dry for it to germinate. Another survivor from a livelier past is the wild mountain sheep with immense curved horns that share its arid habitat with jerbils, and with a wheatear which builds a nest that can cope with the desert climate.
Once, however, the plateau supported a very different fauna. There were giraffes and antelopes, Hippopotamuses, lions and elephants -even men and women who lived by herding cattle and goats. Some of this is known from ancient animal bones dug out of the sand, but far more evidence comes, irrefutably and uniquely, from rock paintings found among the towering cliffs and wondrous rock formations of Tassili N’Ajjer.