Initial Assumptions:
- That all documents are accurate and true.
- That recent parchments are contemporary, and that old parchments are also contemporary.
First we investigate the distant past...
A) Theory; Our ancestors mined into the Earth and discovered the Underworld. The Underworld is protected by a Guardian who sent forth Demons to drive our ancestors out. Our ancestors managed to seal the entrances to the Underworld and swore never to return.
Evidence; A book (The Guardian's Wrath). (Ref: L02/018/a).
Notes; The book states that Demons were sent forth to drive our ancestors out and hunt them down, rather than simply hunt them down and drive them out. The book also refers to entrances to the Underworld rather than a single entrance.
B) Theory; There was a cult dedicated to the worship of the Guardian. The Guardian is known as the Keeper of the Dead. The Guardian is responsible for the care of our dead, and possibly giving them life beyond this life. A prophecy exists, that in a time of dire need the Guardian will raise an army of the dead to defend us. The Guardian is our protector.
Evidence; A book (The Guardian Of The Underworld). (Ref: L02/018/b).
Note; Given the prophecy we can assume that the Guardian is not simply responsible for watching over our dead, but is in fact our protector.
C) Theory; The architects of Level 4 were members of this cult, known as the Conservers. A significant function of Level 4 was storage for vast numbers of documents. Either the Guardian, or his avatar, takes the form of a spider. The Demon on Level 4 was sent forth by the Guardian to protect the Underworld from intruders.
Evidence; A parchment (old) found east of Papin's rooms on Level 2 reads; "I have been informed that the conservers have spies amongst us. Despite our differences I cannot imagine that they're looking to harm us, or even impede our mission here. I cannot in truth see much reason to prevent them from knowing our progress, I am inclined to just let them get their information rather than waste resources and encourage doubt and suspicion amongst us." (Ref: L02/022).
Clearly the architects of Level 4 were competent builders and their beliefs and duties are reflected in the design of the area, which (as we know it) is in part a massive library. The primary symbology is that of a spider. Given we know the Conservers worshipped the Guardian, and their primary symbology is that of a spider, then we can assume that the Guardian is the spider.
Since the Demon was encountered on Level 4 and the Guardian is the only entity (we know of) with the power to send forth a Demon, and considering our location (probably deep underground) and history (#L02/018/a), then presumably this Demon is as described (in The Guardian's Wrath).
Notes; The Guardian's Wrath states the Guardian sent forth Demons, rather than a single Demon. The Demon found on Level 4 (aka Sir) could be one of the original Demons. Its behaviour (to attack on sight) appears to conform with its task as set by the Guardian.
D) Theory; The architects/occupants of Level 4 were from the same civilization as the architects/occupants of Levels 1 through 3. The occupants of Levels 1 through 3 communicated with the occupants of Level 4, although they had their "differences". Engineers from this civilization operated across all four levels, and their origin was Level 4. This civilization was our own ancestral civilization.
Evidence; Clearly the occupants of Level 4 were in contact with the occupants of Levels 1 through 3 (#L02/022) and spoke the same language (or could at least translate).
Two individuals operating on Level 1 (Darrin, possibly the commander, and Naiss, an engineer (#L01/016/b)) have names similar in style to an individual operating on Level 4 (Dassin, presumably the head librarian (#L04/038)).
The blue lights found across all four levels (whilst not identical) were almost certainly constructed using the same process, and probably by the same engineers (from Level 4), given the design of the lights on Levels 1 through 3 is reminiscent of styles and symbology originating on Level 4.
Given we can read and understand (most of) these documents then we can assume this civilization comprised our own ancestors.
Notes; If the "spies" from Level 4 could not blend in then they would presumably be of little use. The occupants of Levels 1 through 3 appear to have been primarily soldiers, and the occupants of Level 4 appear to have been primarily cultists/bureaucrats.
E) Theory; Engineers from Level 4 built the Portal. The Portal was the primary means of interaction between the occupants of Level 4 (Conservers) and the occupants of Levels 1 through 3 (the "Soldiers"). The Portal was used to move a significant quantity of material and supplies.
Evidence; Level 4 is covered in a strange regular symbology, part angular, part curved. The Portal itself is part angular, part curved. The similarity is overtly obvious, including (but not limited to) the symbology adorning walls, the design of the spider (especially the body), many designs on the Conserver Council's Table, chairs, torch-fittings, and gates. In numerous cases the design of the Portal is strikingly similar to the symbology found on Level 4.
Given the Portal exists and connects Level 4 to Level 3 then we can assume that this is how they travelled and communicated. The extensive storage facilities and huge volumes of supplies on both sides of the Portal imply that the Portal was also used to move a significant quantity of material.
Note; It is not clear in which direction the supplies and material were moved, or the purpose of doing this. Nevertheless, given the scale of the endeavour, we can speculate that the reason was either offensive, defensive, or construction (or any combination thereof).
F) Theory; Trouble was brewing on both sides of the Portal. The Soldiers (on Levels 1 through 3) were facing a threat from the outside. The Conservers were experiencing some form of internal dispute (Terschenn was doing something that not all Conservers agreed with). At some point violence occurred on Level 4 (#L04/034/a). The Demon somehow got into Level 4, which would account for the violence. It seems likely that the release of the Demon was linked to Terschenn's activity.
Evidence; A book found in the court room on Level 2 (east of the armoury) is a log filled with detailed reports of people violating certain rules. Most of these rules are obviously aimed at preventing the entry of intruders. They are strict and elaborate to the point of seeming a product of paranoia. (Ref: L02/017).
A parchment (old) found near the vault on Level 1 states "In response to our surprising failure we've installed Naiss's ingenious mechanism as a final precaution against intrusion." (Ref: L01/016/a).
The huge door in the south of Level 1, possibly the main entrance, has been barricaded. This implies the occupants expected to be attacked from outside. (Ref: L01/008).
There is a large map on Level 2 (northwest). Two positions on the map (in the north/south hills) describe "watchers" which implies some level of threat, and indicates the map is being used for (potential) military activity. (Ref: L02/019).
A parchment (new) inside a desk in Papin's rooms (on Level 2) states; "Clearly this was once a place of military activity, but who were they fighting? Were we once at war with these people? It would seem we won. How could such events be completely erased from our history?" (Ref: L02/020/b).
(#L02/022 - see above).
East of Papin's rooms on Level 4 are two (old) parchments:
"Venerable Aderon, I understand that you are conflicted, but I must ask that you keep the voicings of your misgivings to within the council. You cannot hope to stop this now, you will only cause disquiet and potentially worse. Please remember the responsibility that comes with your position. Terschenn." (Terschenn is presumably the head of the Conserver Council). (Ref: L04/035/a).
"Our glorious hero is little more than a killer. Now that his deadly work is done he cares nothing for the consequences. Murder our gods so that we may be free. And lost. I will not forget who saved us from oblivion. We have been warned, far worse is coming and our demise is now inevitable." (Presumably written by Aderon, a Conserver Council member). (Ref: L04/035/b).
A parchment (old) on Level 4 inside a cabinet in the southwestern end of the library; "Burn, burn it all! A lifetime watching over things that I must now consign to the fires. For what? The teachings of a monstrous traitor? The sorry truth is that no one is willing now to admit they were wrong, too much was invested, it couldn't be for nothing. And so we go forth and burn the path behind us, let blind hope be our guide." (Presumably written by Dassin, head librarian). (Ref: L04/039).
A parchment (old) found on a skeleton wandering Level 4 (west); "When I took this oath I told myself my life no longer mattered. Now that courage, that sense of purpose, is fading fast. I look to the others for strength, but I find the same doubt in their eyes. They mocked us and now I see the truth of it. This is senseless." (Presumably written before his body was resurrected by Papin). (Ref: L04/040).
Extract from a (new) parchment found in Papin's rooms on Level 4; "These dead guards, perhaps I could call them into action." (Ref: L04/034/a).
Notes; It does not appear that the external threat managed to breach Level 1, assuming the barricades (#L01/008) are old rather than recent. It is unclear whether the Conservers and Soldiers ever fought amongst themselves (given they seem to have been cooperating, despite their differences). On the War Map in Level 2 is marked a position referred to as "UnderEarth", which could well be our current location (at least before we used the Portal).
Summary:
- Our ancestors discovered the Underworld, a place hidden deep inside the Earth.
- A Guardian protects the Underworld.
- The Guardian sent forth Demons to drive our ancestors out.
- Our ancestors sealed the entrances to the Underworld and swore never to return.
- There was a cult dedicated to the worship of the Guardian.
- The Guardian is known as the Keeper of the Dead.
- The Guardian is responsible for the care of our dead, and giving them life beyond this life.
- A prophecy states that the Guardian will raise an army of the dead to defend us (i.e., the living) in a time of dire need.
- The Guardian is our protector.
- The architects of Level 4 were members of this cult, known as the Conservers.
- A significant function of Level 4 was storage for vast numbers of documents.
- Either the Guardian, or his avatar, takes the form of a spider.
- The Demon on Level 4 (aka Sir) was sent forth by the Guardian to protect the Underworld from intruders.
- The architects/occupants of Level 4 were from the same civilization as the architects/occupants of Levels 1 through 3.
- The occupants of Levels 1 through 3 communicated with the occupants of Level 4, although they had their differences.
- Engineers from this civilization operated across all four levels, and their origin was Level 4.
- The occupants of Levels 1 through 3 were primarily soldiers.
- The occupants of Level 4 were primarily cultists/bureaucrats (Conservers).
- This civilization was our own ancestral civilization.
- Conserver engineers built the Portal.
- The Portal was the primary means of interaction between the Conservers and the Soldiers.
- The Portal was used to move a significant quantity of material and supplies.
- Trouble was brewing on both sides of the Portal.
- The Soldiers were facing a threat from the outside.
- The Conservers were experiencing an internal dispute.
- At some point violence occurred on Level 4.
- The Demon somehow got into Level 4, which would account for the violence.
- Terschenn's activity explains the release of the Demon.
Conclusion:
It is probably best to leave things there for now. Of course we could speculate that survivors from Level 4 (and perhaps Level 3) escaped deeper into the Underworld, but this is probably premature given we haven't yet seen the whole of Level 4. We might also speculate that construction of the Portal did not itself constitute a breach into the Underworld (although it might have been part of such a plan), but pffft, who knows? We need more data.
We could even speculate that the Conservers attempted to kill the Guardian itself (or its avatar), but let's not even go there...