A long time ago, some time around the 13th century, as Venetian merchant and explorer Marco Polo crossed the Gobi Desert, he thought he heard the voices of restless spirits.
Polo has been recorded as saying: "… when travellers are on the move by night, and one of them chances to lag behind or to fall asleep or the like, when he tries to gain his company again, he will hear spirits talking. Even in the daytime, one hears those spirits talking. And sometimes you shall hear the sound of a variety of musical instruments, and still more commonly the sound of drums."
