From From President To Prison from Ferdinand Ossendowski an idiosyncratic retelling of 10th- to 12th-century Northeast Asian history (the guy is just like a proper historian!):
In the course of my business, I made the acquaintance of the richest merchant of the town and heard from him some interesting law regarding these Kara-Khorch’ins. He told me that this tribe had often swept down toward the Great Wall,