I didn't know about this, but there is some evidence suggesting that a particular legion in the Romany military (on the losing side of things) ended up in China and founded a city there. It's #4 on the list of “History's Most Overlooked Mysteries”.
The Parthians pretty much spanked the Romans every time they tried to move east. Crassus lost an entire army in the east at the Battle of Carrhae in 79 B.C. and died to boot trying to invade the Parthian Empire. That is the source of my disbelief of the myth. The story also sounds like an episode of the Ten Thousand out of the “Anabasis” of Xenophon.
I was doing some reading about the Battle of Carrhae (in 53 B.C.) and so it seems as if the legend of the “lost legion” is at least plausible. In answer to Skiguy's question, this legion would have been captured in the battle by the Parthians and relocated further east. From what I read, the Chinese later captured land held by the Parthians.
I think the story is at least plausible. There is a story recorded in a number of places that during the Normandy invasions the Americans captured some enemy soldiers who spoke no language that anyone could recognise. That was until a British NCO who had served in India heard them and understood what they were saying. It turned out that they were from southern Russia near to Afghanistan. They had been captured by the Germans invading Russia and carried a third of the way around the world to fight in a war which they presumably had only the haziest idea of.
The whole idea that there was a “Lost Legion” captured at Carrhae and transported to the east assumes that the Parthians kept the Legion together after their capture. Why would they do that? It is much more plausible that nay Legionnaires captured were immediately either executed or sold into slavery. I cannot think of a good reason for them to keep them together. If anything Romans were known for being fiercely loyal and that argues strongly for the disbandment if not execution of any legion captured intact.
I dont see how linguistic spread speaks to a specific incident involving a Roman legion. This is especially so given that texts in Tocharian (the language you cite) all date from the 6th to 8th centuries AD, one would expect that if the Language was descended from even vulgate Latin that earlier texts would be extents since it is reasonable to assume that many legionnaires were literate. Literacy may not have been universal in Rome but it was common, the amount of Graffiti in Pompeii and Herculaneum attest to that. UT has a pretty good page dealing with Tocharian and many other old languages.
Tocharian has nothing to do with Latin but about Indo-European migrations. This happening long time ago before Rome even started raising as a significant power. The lost legion theory is totally irrelevant.
People and peoples have been migrating for thousands of years for many different reasons. In fact, the largest human migration in history happened lss than 100 years ago. I wonder how many of you guys can say what it was?Wouldn't linguistic spread be a better measure of cultural dominance than the movement of people?