There was another danger to which they were exposed in their march, more terrible even than the scarcity of water. It was that of being overwhelmed in the clouds of sand and dust which sometimes swept over the desert in gales of wind. These were called sand-storms. The fine sand flew, in such cases, in driving clouds, which filled the eyes and stopped the breath of the traveler, and finally buried his body under its drifts when he laid down to die. A large army of fifty thousand men, under a former Persian king, had been overwhelmed and destroyed in this way, some years before, in some of the Egyptian deserts. Alexander's soldiers had heard of this calamity, and they were threatened sometimes with the same fate. They, however, at length escaped all the dangers of the desert, and began to approach the green and fertile land of the Oasis.