Take a Roman legion, greek phalanxes, eastern spearmen and ranged firepower, and ram them all together. Remeber how the best thing about Rome in the grand Campaign is the auxiliary barracks, allowing you to flesh out armies with units from other races? Well Palmyra gets that, AND its basic unit chains have some of that diversity as well. The empire was multilingual, multicultural, and essentially a hodgepodge of everything in the area.
Palmyra’s burgeoning empire stood at a crossroads – part of the Roman Empire, jammed between Persian, Arabic, and Egyptian cultures, with Galatians to the north and a history of Greek culture thanks to Alexander and the later Seleucids.