>>96497344
I'm only a hobbyist level Romaboo, but I tend to avoid secondary sources like the plague. Everyone has an agenda (even the primary sources typically do, but at least that's only one agenda you have to account for, not two or three). I mostly study Greco-Roman theology and mythology as part of my comparative studies (I'm really more of a holistic Euroboo) and for RPG inspiration, so that's your Homer, Hesiod, Ovid and Apollodorus and their sort. Herodotus is a really good source of inspiration to populate a sword and sandal RPG setting, since he describes all sorts of less well known ethnic groups. For specifics on Roman history, I think Livy is considered the go-to guy, but I could be wrong. For opinions on western European barbarians, Caesar, Tacitus and the anything on the Cimbrian War comes to mind.
If you're a visual sort of guy, then the Osprey books are the ones with the consistently most appealing illustrations I've found. Nothing beats a trip to the museum and glyptotheque though.
Hope this helps, and don't hesitate to ask any questions. Maybe Romaboos of higher power levels can also add their two sesterces.