Training Foreign Troops-Roman Evidence?

[Titus Labienus]

I was discussing with a friend the current discussion in the United States to arm Syrian rebels in the fight against ISIS. Does anyone know of an instance in Roman history (say from 509 B.C. through A.D. 476) in which the Roman army ever trained or equipped foreign troops to deal with a distant conflict that could have been seen as a threat to Rome's interests? In other words, did Rome ever do anything like what we have done/are doing with regard to equipping/training foreign troops, or did Rome always send in legions and do it herself?

This is not to be a political debate on contemporary issues, but merely a discussion of ancient responses to distant conflict.

Thanks!