Hello, @Sylvermynx! So, the year started (Happy New Year to you once again!) and now we can finally see the answer to your question about that monolith. @Thevampirenight was absolutely correct saying that "its tied into the New Life festival. They are doing a new Imperial quest for the New Life. So that might explain why that Shrine is suddenly there. I won't spoil the quest or anything other to say that its connected to it."

The monolith turned out to be the Old Life shrine. But the lore the devs wrote made my theory I wrote in this reply above in October relevant too.

First, I was right here it was an Imperial monolith, and that it was indeed a remembrance shrine to honor the dead: Petronius Galenus - "Old Life is an Imperial tradition. At year's end, we write messages of remembrance for our dead loved ones in hopes that our words will reach them in Aetherius. You must light a candle at a shrine dedicated to the Old Life and write a short message to one who has passed on. Most shrines have parchment available. Then, you simply pass your message over the flame. The Old Life ceremony is deeply personal, but those who participate feel a sense of connection. As I'm sure you felt. Many have lost loved ones in the process, after all.
Their shrines were destroyed within Imperial City. As they relocate, many have given their messages to people like me, hoping they will reach a shrine elsewhere in Tamriel".

Secondly, these words of Petronius Galenus also give us a cue that these shrines could also be construceted by common people to remember those who were dear to them. That makes my idea of that particular shrine's origins you asked about still relevant - it all really suits a possible story that Accalia built that monolith during his reconstruction of the Fort defenses in honor to his aunt who was the only reason of his power and wealth. He could have constructed the monolith right on the place of his aunt's hut that saved him life and allowed to become richer. The hut could be supposedly destroyed by the mercs and militia who "swept the hills clean" while Accalia was away, but he was very grateful to his aunt who left some money and her hut on that hill - the reason of all his further rise (and actually fall).

Thirdly, even if it was not Accalia, my very first idea that the monolith could have been built by the Imperial Legion builders (this post) turns out to be possible too: "the monolith was built either in 1E 2703 - 1E 2840 (after the foundation of the Reman Empire and it's conquest of Elsweyr, but before the Reman II war against Morrowind) or some time after 2E 430 (152 years ago), after the fall of the Second Empire when an Imperial Legion stationed there abandoned the keep". Though, yes, I was totally wrong in my very first initial idea that the reason to build that monolith in the first case could have been to create a landmark for the keep's defensive trebuchets artillery spotting, in the latter - to commemorate the end of the Imperial official presence in the region. It turned out to be absolutely wrong due to the purpose of the monolith we now know of.

So, as I have said it in October, I think it's a remembrance shrine built either by the local Imperial Legion in either in 1E 2703 - 1E 2840, or some time after 2E 430, or recently by Accalia.

P.S. The question about that jerboa is still a mystery to me . Perhaps, it's time to dig into it since the question about the nature of the monolith is clear now.