You wouldn't happen to visit /r/china do you? This topic popped up today.

For those of you not privy, the theory is that after the Battle of Carrhae in 53 BC against the Parthians, the surviving legionaries were sold into slavery to the East. They then settled in a town called Liqian, supposedly a corruption of the word "legion," which is why the inhabitants of the area have large noses and fairer hair.

Homer H. Dubs, the man who first put forth the theory, was a professor at Oxford and is very credible. However, this theory is very controversial and is very unlikely. To quote wikipedia:

Several investigations have been conducted since.[3] Rob Gifford commented on the theory and described it as one of many "rural myths."[6] One DNA study found that "a Roman mercenary origin could not be accepted as true according to paternal genetic variation, and the current Liqian population is more likely to be a subgroup of the Chinese majority Han."[7] Genetic testing in 2005 revealed that 56% of the DNA of some Zhelaizhai residents was Caucasian in origin but the testing did not determine whether they were descended from Romans, Tocharians or Iranian peoples.[8] People with Caucasian-like traits existed in central Asia centuries before the Romans; Tarim mummies and some south Siberian populations included light-haired individuals.[9] To date, no artifacts which might confirm a Roman presence, such as coins or weaponry, have been discovered in Zhelaizhai.[5]

As much as I would love the idea of a Roman legion in ancient China, there is just not enough evidence to completely support this idea. There are no Roman artifacts or remains or anything to suggest that they inhabited the area. It's definitely an interesting idea though. I think Jackie Chan is actually filming a movie on this topic right now.