Interesting article...

There is quite a bit to suggest that the East West trade route into China has been around for a lot longer than people believe. If people could travel the waterways of Europe some 6000 years ago to trade then its highly likely they also went further afield.

One theory reloves around early domestication of horses which enabled huge distances to be travelled...

Anyway, here's the info, much more on the web if you go looking...

Caucasians in China: The Takla Makan Mummies Page 26