Executive producer Julie Plec spoiled at Comic Con that there were chunks of witch mythology left to tell. The fabulously cryptic Plec, elaborates on what we can expect in season 4 and beyond.
“To clarify what I said [at Comic-Con] … when Esther used that spell to make her children immortal, which created the Original vampires, that spell existed already. So who wrote it? That’s the question that will remain a question in this season and possibly in the series. We dabbled with the Original vampires, but who were truly the Original witches?”
Source: TV Guide