Windblown dust

In 525 BCE, according to Herodotus, the Persian king Cambyses II assembled an army of 50,000 men to march across the Egyptian desert to subjugate the priests of Amun.In her futuristic time travel novel And the Rest is History, Jodi Taylor places her protagonist Max and a companion perched among boulders in the western desert to witness the army's march toward the Siwa Oasis.Max spies a "dark yellow murky cloud" where the horizon had been and hopes that it is dust "kicked up by a marching army rather than the beginnings of a sandstorm." 1 No such luck.