They kept leaving all the time. One from a town, two from a family, they fled the settled districts of the land of Egypt to join those who had left before them. They did not go far: no further than the nearest oasis or the first gully that had a spring. They sought only to put the sand between themselves and Egypt, to get away from its lords and officials. No more than that.
They had no leaders. Perhaps no customs either. They dwelt in their oases, where they led lives of lowly, grinding, sunbaked poverty, shuffling about in black rags, whistling to their flocks that were as black and gaunt as they, often subsisting by robbery. Now and then troops were sent out to restore order; yet this did not happen often, for such expeditions were known to be perilous. The barefoot oases-dwellers could deal the soldiers a quick, sharp blow and melt off into the sands where even the wind lost all track of them. Year after year the corpses left by both sides were scorched by the sun until they could no longer be told apart from the bones of the earth itself. Every bit of yarn or iron had been stripped from them long ago.
Thirst: The Desert Trilogy