The Books of the Elements combine Roman culture with regional myths, but I don't mean regional religions. I'm building on African backgrounds and folktales in Monsters of the Earth, but there isn't a Pan-African mythology.
Besides the folktales, I'm using African history as told by Herodotus, a Greek historian of the 5th century bc. When Herodotus was writing about his own time and place, he used first-hand evidence and is as good a source as anyone could be. When he's dealing with the interior of Africa in what was the ancient past even to him, he's telling myths--and that's perfect for me. The Books of the Elements are fantasy novels, not historical novels with bits of fantasy dropped in here and there.
My undergraduate majors were History and Latin, and I translate Latin poetry on my website for fun. Although I'm deliberately calling the capital city Carce rather than Rome to drive home the fact that these aren't historical novels, I'm using my life-long interest in classical culture to create a background very similar to that of Rome in 30 ad.
When I describe the house in which the dictator Sulla lived a century before the action of my story, it's in the right place. And when I describe the heads of thousands of victims of Sulla's Proscriptions being displayed in that house for identification, that's true too. I'm writing fiction, but I'm doing my best to describe a real culture and people who think and act like those who really lived in that culture.
Writers have to make tradeoffs in dealing with a foreign culture (the Latin word for foreign is alienus, and "alien" describes the problem better). Some writers pretend that Roman culture (for example) was a lot like our own though with less technology. (Indeed some writers are so ignorant that they think foreign cultures really are just like our own. Politicians are even more prone than writers to that stupidity.)
The other alternative is to use characters who think and act pretty much the way Romans did act--and to hope that readers won't be put off by being asked to identify with people who think and act in ways that nobody today would think or act. The Roman economy was built on slavery, so some of those ways can be horrifying to a modern American. (A decent one, at any rate.)
I try to show what I believe is the reality. I don't rub readers' noses in the worst kinds of brutal cruelty, but I don't pretend they aren't there. (Remember the way Sulla decorated his home?)
More to the point, my characters are no more horrified by the ordinary realities of their own time than you or I are horrified by people who drive two blocks to the grocery store instead of walking or taking public transit. We may wish things were different, but it isn't something that concerns most of us very much.
There's a further influence on Monsters from the Earth which deserves special mention: Virgil. There was a real poet named Publius Vergilius Maro, who wrote the Aeneid and other major poems. There was also a mythical Virgil the Magician whose life was based on that of the poet but who also controlled demons, knew the secret of eternal life, and defeated vast armies through magic alone.
This was such a formative myth that even today (particularly in America) the poet's name is generally spelled Virgil instead of Vergil. A magician's wand was a virgilla, so the poet's name was changed in manuscripts to reflect his believed connection with magic.
I've woven in the wonderfully varied stories of Virgil the Magician. A reader doesn't need to know anything about the Virgil myth (or about Herodotus, or about Roman culture) to enjoy Monsters--but readers who do know a lot on any of these subjects will be amused (and I think pleased) to see what I've done that the material in my story.
Finally, languages and cultures change, but I believe the choice between Good and Evil remains constant. There's no question in Monsters of the Earth that the viewpoint characters are on the side of Good--even if their path to Good is across some pretty rough territory.