From "The Travels of Marco Polo"

...After those three days of desert [you arrive at a stream of fresh water running underground, but along which there are holes broken in here and there, perhaps undermined by the stream, at which you can get sight of it. It has an abundant supply, and travellers, worn with the hardships of the desert, here rest and refresh themselves and their beasts.]…

…Now, if we go on with our journey towards the east-north-east, we travel a good forty days, continually passing over mountains and hills, or through valleys, and crossing many rivers and tracts of wilderness. And in all this way you find neither habitation of man, nor any green thing, but must carry with you whatever you require. The country is called BOLOR. The people dwell high up in the mountains, and are savage Idolaters, living only by the chase, and clothing themselves in the skins of beasts. They are in truth an evil race.