While playing The Elder Scrolls: Online, I came across a lore book. It was titled
Ruminations of The Elder Scrolls
As some may know, this book was written by Septimus Signus, a former College of Winterhold member. He wrote this after his madness consumed him (which was caused by his reading of an Elder Scroll). In Skyrim, on your search for the Elder Scroll, you read a book offered to you by Urag gro-Shub, an Orc who works as the librarian for the College's sizable library. When read, you speak to Urag, stating that the book is "incomprehensable". Urag then states that the book was written by Septimus Signus. after some extra dialogue, Urag tells the player that Septimus is possibly north of the College, so the player goes to investigate. The Elder Scrolls: Online takes place in 2E 582, while Skyrim takes place almost a millenium later, in 4E 201. Sepimus could not have written it in the second era since you get to meet him in his outpost, and he could not have lived that long, as it would have been written more than 1000 years before. So the main question is: Has Septimus Signus time traveled back to the second era? Or maybe did he come from a time much longer ago... or is Septimus Signus immortal? Has his reading of the Elder Scroll somehow caused to achieve unlimited life?
You know, the "Septim" in his name makes me think of Tiber Septim, coincidence, or an interesting choice of psuedonym, maybe he came down to take matters into his hands, from his realm of Aetherius, or maybe he's a descndant.
I don't think Septimus himself time travelled, but there have been instances before in the Elder Scrolls of books appearing many years before their publication. Also, the wiki states that his name is derived from a latin phrase meaning "The Seventh Sign", so I don't think he's related to Tiber Septim, rather I think it's some sort of reference made by the devs that I don't understand.