Lore
The deep was originally a peaceful and sacred place, but became the final resting place for many abhorrent things. Terrible things are said to slumber in the Cathedral.
The Deep corrupts. Those who linger near it often slip into its darkness and are intoxicated by its peril. In time, those dedicated to sealing away the horrors of the Deep succumbed to their very power. It seems that neither tending to the flame, nor the faith, could save them. So, the Deep is not necessarily full of malicious intent, but corrupts simply by being.
Theories
The Deep is actually Ash Lake
The Deep Protection miracle mentions that the Deep :
- was a sacred place
- was a peaceful place
- became the final resting place for many abhorrent things
This list fits the description of Ash Lake to a tee, considering how Ash Lake : housed a sacred site for Dragon worship, was one of the most peaceful places in Dark Souls, contained skeletal remains of unknown beings and held a population of abhorrent creatures (hydras, basilisks, man-eater shells). Aside from that, the dark blue hues of Ash Lake matches the color scheme of the Deep perfectly.
But the most important detail would be the vast ocean found in Ash Lake.
This would be where Aldrich's Age of the Deep Sea comes from : he's attempting to raise the ocean's water level through a long sedimentation process via human dregs and stagnant souls.
The Deep is like The Gutter and Shulva
While once a “sacred” place, eventually, trash and refuse made their way down there and “polluted” its sanctity. This is similar to the Japanese concept of kegare, which may be the basis for the vermin in Bloodborne. Kegare, which is a Shinto term, is a “spontaneous reaction to amoral natural forces”, and does not care if the action was deliberate, which marks it as different from sin; it just is. The miracles of the Deep (Gnaw and Dorhy’s Gnawing) summon insects, once more reminiscent of kegare and how Bloodborne chose to portray it, with Dorhy’s Gnawing saying: "Those who linger too long on the brink of the Deep will often slip. Dorhys is sure to have wallowed in this darkness, intoxicated by its peril." This further elaborates on the idea of kegare polluting the world around it. The Deep, by its very “tainted” nature will continue to draw people and things down a hideous path.
The Metaphysics of the Deep, and What Lurks Within It
To understand The Deep, we first must understand the metaphysics and how they play into the origin of the Dark Souls world as well as the strange obsession with Divinity and Bloodlines that the third installment is so enthralled with. We'll start from the beginning. To begin, however, we have to go back - back to a time of archtrees and everlasting dragons… The world as we knew it is described as such when we are introduced: "In the Age of Ancients, The land was unformed, shrouded by fog. A land of grey crags, archtrees, and everlasting dragons." This is the beginning of the world as we understand it. It is essentially a null state, devoid of change. Static; Grey. Trees, grey, and dragons are essential elements we are given that represent the static state of nothingness in which the world begins.
"But then, there was Fire. And with Fire, came Disparity." Thus begins the world as we know it. Fire, the First Flame, is the core of all action and reaction, and ignites a dynamic world into motion. it is important to understand that before this point, Life and Death did not exist as we understand it. And, of course, as all things set themselves in opposition, so too must Fire have its own. Thus, begins Dark: the shadow cast by the light of Flame.
"And found the Souls of Lords within the Flame." Thus are born the First Lords; creatures stumbling in from the Dark, the origin of life, are drawn to the Flame from the start and in it, find purpose and identity. Nito, Gwyn, The Witch of Izalith & her Daughters - and the Furtive Pygmy. This post is not designed to accommodate deep speculation on the Pygmy; instead, simply realize that these Lords all came from the Dark, and in the Fire, found Souls.
The Pygmy, of course, found the Dark Soul - a special soul. One born of the Dark, not of the Fire itself. While the other Lords became as Gods to a newly born world, he instead created Humanity from his Soul, fragmenting it into so many pieces. This gradience becomes key later, so remember it. Humans are essentially the most finite, smallest fragments of the Dark Soul which can maintain basic cohesion as a being, based on what we've seen from previous games. Limited or not, however, humanity is collectively the Dark Soul at all times. What does this mean? Self-action.
Gwyn was said to "tremble at the coming of the Dark", and he rightly feared the humans who were born of it. While his Lord Soul was of the Flame and made him as a Father-God to the Age of Fire along with his fellow Lords, it was finite, as all Fire is.
To understand this, conceive of the "Soul" as the energy behind creation, the counterpart to the inert matter of the Age of Ancients. A post previously on another Souls reddit I can't locate know identified something important; souls can become matter and matter become souls with the right tools. Thus, souls are both energy to the Souls Universe and the metaphysical force behind action itself: the Lord Souls were and are self-action, the means for individuals to affect change upon reality, just as the Fire is the producer of all tandem forces working in cooperation and opposition, and itself opposed by the Dark. Again, this is a bit of fancy metaphysical postulating, but it's the method one can read into to understand the underpinnings of our main topic.
As the Fire faded, as it was wont to do, being destruction and creation feeding upon itself, the fire fades. What would come next has been defined as "the Dark", or "The Age of Dark", or "The Age of Humanity". While there are some differences to these, the essential idea is that the time of humanity and the fading of the flame are in tandem. This is what Gwyn feared most; his own fading with the Flame, being of a Lord Soul of the Flame. So, he Linked the Fire. But what was the linking? We know he became a Lord of Cinder, and that it prolonged the Age of Fire, but we can't really understand what happened without a broader angle across all three games. In short, if you've played them, you've been witness to a slow and confused death. Gwyn broke reality.
With the Age of Fire came Disparity, and disparity produced something to opposite infinite - finite. Thus, by its very nature, it was to naturally fade to an Age of Dark. While the following is entirely my interpretation, I see this "Dark Age" as being the entropy death of the reality we see in the Souls universe, and a new order asserting itself. Or, you could say, the Old Order - the Age of Ancients. That is, a three-Age cycle in which the world turns to grey ash, the light grows dim, and eventually nothing is left but static nothing. Until, once again, Fire and Disparity appear.
The point is that there was a natural cycle which Gwyn destroyed by Linking the Fire. While we cannot say what exactly he did to start this curse, Humanity is inextricably linked to it. The Flame, instead of producing Souls as "heat" like a normal flame would, has been inverted to consume the very heat it produced as a source. Quite literally, Gwyn attempted to make causality run backwards. The result is the world we are given; time and the barriers of reality have broken down as the Flame fades. This is why we encounter the Undead, and figures epochs apart meet and lands converge at impossible points, and nothing is good or sane. Remember this - Gwyn made it impossible to truly ever enter an Age of Dark, shattering the very cycle of the world in a broken daisychain of fading and linking, corrupting reality and creating the ruin we see.
The essential concept is that things have changed. This is the penultimate result of the Linking of the Flame, and the lack of a true Age of Dark; a perverse land full of undying, insane monsters where the sun disintegrates in a molten stream in the sky and hollows turn into trees. Most importantly, it is choked with Ash: the formless, inert dust that is the result of Fire's progress. For such an extreme situation, the ash is collected, and births the Unkindled. The Unkindled, essentially, are reassembled fragments of humanity held together with the essence of Flame (Embers) for a singular purpose: to Link the Flame where no Lord can be chosen. Yeah, your character? A pile of reanimated dust with skin.
But what does this have to do with The Deep? Everything. The most telling identification of the Deep comes from the Soul of Aldrich itself: "When Aldrich ruminated on the fading of the fire, it inspired visions of a coming age of the deep sea." Deep Sea and Deep are essentially the same in Kanji. Aldrich's timeline is very murky, as to when he became "Saint of the Deep" and established the "Church of the Deep", and when he became the Devourer of Gods. This is secondary to The Deep itself. What is important is the other information we're given about it. Most interestingly, that the Deep was "sacred" or "peaceful" before some vague corruption via defilement according to the miracle Deep Protection: "The deep was originally a peaceful and sacred place, but became the final rest for many abhorrent things. This tale of the Deep offers protection for those who worship amidst those horrors."
The Deep Ring identifies the corrupting nature of the Deep's monstrosities upon mankind and the need for defense against it: "In the Cathedral slumber things most terrible, and as such, the deacons require a grand narrative, to ensure they do not falter in their duty. A philosophy, to ward away the madness beckoned by the grotesqueries at hand."
The Deacon Set also identifies neither Faith nor Flame could prevent this corruption from taking place: "In time, those dedicated to sealing away the horrors of the Deep succumbed to their very power. It seems that neither tending to the flame, nor the faith, could save them."
So what do we know about the Deep as it stands?
- Aldrich has dreamt of is coming Age, after the Age of Fire.
- It was once peaceful and sacred before being defiled and becoming a dark place
- It is populated by abominations, and this corruption is prone to spread to mankind
- Neither Faith nor Flame can deter this corruption; the power of Fire or its Lord Souls cannot stop it.
This all sounds a lot like the Abyss, doesn't it? The creatures associated with The Deep even have red glowing eyes like Abyssal aberrations from previous titles, and the Farron Greatsword which does more damage against Abyssal denizens affects those of the Deep faith and its products. What's the difference, then? One item description, from the Deep Gem: "…Found in the dregs of the Cathedral of the Deep. …There is a darkness that lies beyond human ken." What could that be? The answer is the Dark itself. More specifically, the Abyss. The Abyss born of a corrupted world.
Consider for a moment that humanity and all beings we are familiar with dwell in the world of Fire; of light. Even when the Sun is down, the Moon glows in the night sky. Human worship of deities in the Souls universe is based on the cycle of light provided to us. We are on top of according to the geography of all three games a vast forest of Archtrees, like the greenery adorning its branches facing the Sun. Beneath it? The Dark. Or, more specifically, the Abyss. Just as the Flame produced its counterpart, so a counterpart to our world as we would know it exists. And who is to say that world would necessarily be evil? Could it even possibly be…peaceful? Sacred? This is just spitballing, but the fact remains that when Gwyn Linked the Flame, reality was irrevocably shattered in its natural course. Who can say what the breaking of reality would do to something so alien as the realm of the Dark? Well, we can speculate on that: The Deep.
The Deep is not necessarily a place, or an Age. It is instead a metaphysical concept born of the corruption of reality as the Souls universe currently exists, the corruption of Dark. Just as the Fire fades, Dark wanes, swells, but cannot complete the cycle. Its causality is equally defaced. What comes of that? How can we know? Well, we can't. But we can speculate.
The Deep is nothing more or less than an unfathomable corruption of the Dark into horrible, grotesque forms that defy sanity itself. Something beyond the limited dark of Humanity - beings which are the smallest subgradients of the Dark Soul, living within the Light. Just as the First Flame is an undying shell of its true form, so too is the Dark now a roiling sea of madness and consumption.
Aldrich (being a Lord of Cinder) dreamt of the Age of the Deep, an Age after the Age of Fire. This would be an Age of monsters and Abyssal insanity - not an Age of Men - who are corrupted by it now. Who even first suggested that the Age of Dark was the Age of Men? The Primordial Serpent Kaathe, that's who. We cannot even verify anything either Serpent in Dark Souls 1 told us was true, but the basic framework coincides very nicely with the metaphysics we have established. In truth, maybe Kaathe did not even know that the Flame could not fade out completely to an Age of Dark, having never entered into one with the relinked Flame still smoldering. Or maybe - maybe he has darker intentions. Deeper intentions. After all, the Sable Church of Londor was led by a woman who identifies her driving agent as Kaathe himself, and the architecture of Lothric Castle is lousy with serpents. But what does this mean?
Sources
Soul of the Deacons of the Deep
One of the twisted souls, steeped in strength.
Use it to acquire many souls, or transpose to extract its true strength.
After Aldrich left for the Boreal valley, Archdeacon Royce remained in the cathedral with the high priests, to keep eternal watch over their master's coffin.
Cathedral Knight Armor
Repulsive creatures of the deep are sure to attract the foolish, but the cathedral knights are prepared to meet such intruders head on with their more than ample might.
Deep Ring
A ring bestowed upon the Deacons of the Cathedral of the Deep. Allows attunement of additional spells.
In the Cathedral slumber things most terrible, and as such, the deacons require a grand narrative, to ensure they do not falter in their duty. A philosophy, to ward away the madness beckoned by the grotesqueries at hand.
Deep Gem
A gem of infused titanite. Found in the dregs of the Cathedral of the deep.
Used in infusion to deep weapons.
Deep weapons inflict dark damage, but lose scaling effects.
There is a darkness that lies beyond ken.
Deep Soul
Sorcery of Archdeacon Royce and his deacons, said to have been imparted to them by McDonnell of the Boreal Valley.
Fires dark soul dregs.
Souls which swell from the deep pursue their target, drawn towards life.
Deep Protection
Miracle taught to inaugurated deacons of the Cathedral of the Deep.
Slightly boosts attack, damage absorption and resistance, while also increasing stamina recovery speed.
The deep was originally a peaceful and sacred place, but became the final rest for many abhorrent things. This tale of the Deep offers protection for those who worship amidst those horrors.
Dorhys' Gnawing
Miracle of Dorhys the deranged evangelist.
Summons great insect swarm to feast on foes.
Those who linger too long on the brink of the Deep will often slip. Dorhys is sure to have wallowed in this darkness, intoxicated by its peril.
PREV: Ashen One
The Deep could also refer to some kind of underworld (called "meikai" in Japanese), or like Immaterium of Warhammer 40K Universe. Originally uncorrupted thus peaceful and sacred/pure, over time it became corrupted. It is different from Abyss, which is formed of humanity.
Dreg Heap takes it further. I've came to the conclusion it's humanity of the dead seeking human form again i.e. maggots forming human shapes, murky corpses rising from ashes (of corpses). Human Dregs are a good pointer towards this.