So...I've been trying to do a bit of research on the Nightingales and when they came to be. Or in my case, I'm looking to find out how early in the TES timeline the Nightingales first appeared(but I don't mean literally in the timeline, I mean like a rough estimate of when they could have appeared). There's really not much to go on, to be honest. Reason I'm trying to figure out how early the Nightingales came to form in Tamrielic history is for a lore-friendly OS fan fiction I'm writing.

What I do know, is that Nocturnal is one of the Daedric Princes. Furthermore, the Skeleton Key is one of her Daedric Artifacts. Which leads me to believe that the Twilight Sepulcher, based in Skyrim, had been around for long before the Thieves Guild formed. Which brings me to one of my questions; the Nightingales are considered a subgroup of the Thieves Guild, right? Is it possible that the Nightingales have been around since before the Thieves Guild formed? Like say...since around the time of the early Second Era?

I mean, it makes sense to me, considering Nocturnal's only direct access to Tamriel is through the Ebonmere portal in the Twilight Sepulcher. That's pretty much the only way Nocturnal can come to Tamriel. It's also said the the Skeleton Key has often been stolen from the Twilight Sepulcher many times, which also furthers my reason to believe that the Skeleton Key, the Twilight Sepulcher and the Nightingales have been around for far longer than the Thieves Guild. I mean, the earliest example of the Thieves Guild that I could dig up was about the Gray Fox in 3E 433.

So, in short...my REAL question is along the lines of, "Is it possible that the Nightingales and the Twilight Sepulcher have been around long before the Thieves Guild?" Say...during the time of the Akaviri Potentate rule over the Empire? I'd like to think so.

What do you guys think?