I got to thinking, "what if Rome completely ceased to be?" It was possible -- a massive eruption at Vesuvius could have wiped half of Italy off the map. That it hasn't happened yet is geologic luck -- right now, it isn't a huge threat, but it once was. Had some of the eruptions before 79 CE happened later (they were nastier), Rome... well, maybe not.
Rome had lots of little outposts all over Europe and Western Asia, most numbering a few hundred Romans and a couple thousand locals under Roman guidance. So I got to thinking, what would have happened to those little outposts? Could they have survived and kept the culture alive, if evolving?
And so, the seed of Galantier was born.