The Drapanai and Bastarnae share a model, which probably has something to do with it. IIRC the Getai recruit Thrakioi Peltastai through their factional MICs though, at level 4 or so. I seem to recall the assorted Thracians - Peltastai, those javelin cav guys, and Prodromoi - were spread out somewhat counter-intuitively between their factional and Regional MIC in the relveant provinces; I'd really recommed quicksaving and using the add_money and process_cq [Settlement name] cheats to figure it out, then reloading the save.
Bookmarks