I’m curious though, why callt that the earliest? Going by the dictionary definition of a novel (A fictitious tale or narrative, longer than a short story, having some degree of complexity and development of characters; it is usually organized as a time sequence of events, and is commonly intended to exhibit the operation of the passions, and often of love), there are several ancient works that I’d think would fall into that category (or do epic poems not count?). I just checked Wikipedia and I see there’s a whole article on Ancient Greek novels.