The crumbling ruin of the Fortress of Shali may not look like much today but this mud brick citadel is unique in the world of architecture. The brown walls of Shali aren't made from dirt or clay as you might think but a mixture of rock, sand and salt, called karsheef, that when hardened in the hot desert sun is as strong as brick. Salt, the building material that makes this fortress unique, is the cause of its demise. Salt dissolves in water as everyone knows. And while precipitation is not at all common in this corner of the Sahara, heavy rains have fallen three times in the last century causing the walls of Shali to disintegrate.