Rome in the Client Kingdoms of Bosporus and Palmyr

[ChrisZeichmann]

I'm having trouble finding citations of ancient literature, but I understand that Roman soldiers garrisoned in Bosporus and Palmyra. Can anyone help me out on these two issues:

1) What is the evidence for this (inscriptions, literature, etc.)? Any recommended reading (web sites, articles, books, etc.) on the topic?

2) Why would Rome allocate soldiers to client kingdoms like that?

Any help would be greatly appreciated.