The Pthumerians existed long, long ago, long before the events of Bloodborne take place. And yet the echoes of what happened in old Pthumeru resonate very deeply in the current city of Yharnam, moreso than Yharnamites can possibly know.
The Pthumerian Society existed long, long ago, centuries or even millennia ago. They were a people who were masters of ancient arcane arts, specifically relating to arts of Fire and arts of Blood. The Pthumerian People seemed to be Matriarchal, or at the very least the most important positions were often held by women. The hallways of the ancient Labyrinth echo with the Sinister Bells rung by the Bell Ringers. When we look at the description of a Sinister Root Chalice we are told: "When used in a ritual, this sinister chalice summons the Sinister Resonant Bell. The bell-ringing woman appears to be a mad Pthumerian." Aside from the Bell Ringers we have the Keepers, a group of eternal warriors who wander the Labyrinth caring for its denizens. The Bone Ash Armor states:"The keepers, who mind the slumbering Great Ones, gained eternal life, preserved in ashen form in a ceremony of flame that cremated body and soul." These women clearly held positions of importance, and we do know they are women despite their masks, as the voice clips they play during their combat and death animations are that of a female voice actress.
Finally, we have the Pthumerian Queen. Originally, the Pthumerian people had no ruler, they worked as simple caretakers of the ancient Labyrinth. The Great Pthumeru Ihyll Chalice: "While early Pthumerians were mere humble guardians of the slumbering Great Ones, their descendants felt entitled to name themselves a leader." As Pthumerian society advanced, they grew into a more stable society with a Queen as their figurehead. The capital of Pthumeru, Ihyll, was named after one such Queen, possibly the first. However it is the last Queen of Pthumeru, Yharnam, who will be the focus of our analysis.
As for the men of Pthumerian Society, they seemed to provide more of a workforce and military for Pthumeru. The Hintertomb Chalice tells us: Hintertombs are the peripheral catacombs of the old underground labyrinth. To this day, the Watchers continue to expand the hintertombs, unceremonious catacombs filled with graves and death. Indeed, very often will the clanging sound of a pickaxe fill the Player's ear as the undead Pthumerians toil away to expand the Labyrinth further and further. They are overseen by the Watchers, fat and girthy men wielding cudgels, cleavers, burning irons and even shotguns.
There are also the Shadows of Yharnam; first encountered in the Forbidden Woods, the Shadows are presented to the player far before we know of the Queen's true name. The only two places the Shadows are found are in the Forbidden Woods and in the Nightmare of Mensis, both times in places very close to Queen Yharnam herself. Interestingly enough, if the PC Hunter wishes they can lure the Maneater Boars into the Shadows found in the Nightmare of Mensis. The Shadows will fight and kill the pigs, while some of them will die in the process. The Shadows do not appear to be aligned with the School of Mensis at all. According to the Oxford English Dictionary, the word shadow has many definitions, the most lesser used being An inseparable attendant or companion. It's a very clever use of ironic wordplay by From Software, to introduce the players first to the Shadows of Yharnam, leaving them to naturally associate the Shadows as being associated with the City Yharnam, as opposed to the Queen.
The Pthumerians were, as the Chalices imply, superhuman beings. They were close to the eldritch Truth, and achieved evolution and metamorphosis through the use of blood ministration, as evidenced by the fallen Pthumerian City Loran. According to the Ailing Loran Chalice: "The tragedy that struck this ailing land of Loran is said to have its root in the scourge of the beast." When the PC Hunter travels to the ruins of Loran, they find a city that in many ways resembles Old Yharnam. It is a place ravaged by the Scourge of the Beast, as the vast majority of its inhabitants are either mindless beasts or mad Bell Ringers. There is even a Darkbeast, the mightiest of the beasts, that lurks on the lowest level of the fallen city, just as there is one that dwells in Old Yharnam. In Old Yharnam, the Scourge of the Beast was a result of the rampant blood ministration by the then newly-founded Healing Church in an attempt to cure the horrible disease ashen blood. The Lower Loran Chalice states: "There are trace remains of medical procedures in parts of ailing Loran. Whether these were attempts to control the scourge of the beast, or the cause of the outbreak, is unknown."
We can now put the pieces together and see that what the Player is currently experiencing in Yharnam once occurred a long, long, long time ago in ancient Pthumeru. Through the use of the Old Blood of the Great Ones, the Pthumerians were able to ascend and evolve, and yet with the tainted blood came the Scourge of the Beast, and possibly even what we would refer to in the modern era of Bloodborne as a Hunt, along with a Blood Moon. This brings us back to the Queen.
When the red moon hangs low, the line between man and beast is blurred. And when the Great Ones descend, a womb will be blessed with child. - Note found in the Byrgenwerth Mansion
The PC Hunter first encounters Queen Yharnam after the death of Rom, the Vacuous Spider. The most immediately horrifyingly apparent feature of the Queen is the blood staining her stomach. It's a sickening moment for the player, at least it was for me. She is found at the bottom of the Moonside Lake, having seemingly appeared out of nowhere, staring up at the sky and weeping. There, the PC Hunter sees the Blood Moon for the first time, and hears the cry of a newborn baby. In ancient Pthumeru, the Scourge of Beasts ravaged the land. It must have been then that the Blood Moon arose, perhaps for the very first time, and a womb was blessed with child. It's unknown if Yharnam was impregnated by the Great Ones specifically because she was Queen, or if she was simply a woman chosen at random, but she is most assuredly assumed to have been, in that Hunt, the potential mother of a Great One. As we can see from the bloodstained rags around her stomach, the birth did not go well.
Arianna and the Queen
Let us now jump forwards hundreds of years back into present day Yharnam, and discuss Arianna. The PC Hunter encounters Arianna living in the Cathedral Ward of Yharnam; the Lady of the Night mistakes the Hunter for a potential customer and sends them away, telling them that she takes Hunts off. Once the PC Hunter has defeated Vicar Amelia they can convince Arianna to seek shelter in either Oedon Chapel or Iosefka's clinic. Sending her to the clinic will end all further interaction with her, while sending her to the Chapel will allow the PC to encounter and speak with her further.
Once Arianna and the PC Hunter become acquainted, she does what any good Yharnamite would do and offers her new friend a vial of her blood. If the Hunter accepts, they receive the item Blood of Arianna. It is with this item that we see the first inklings that Arianna may be much more than she first seems. "Blood taken from Arianna, Cathedral Ward woman of pleasure. A member of the old Healing Church would know that her blood is similar indeed, to precisely what was once forbidden." Why would Arianna have blood similar to something that was forbidden? After all, blood flows like water in Yharnam; anyone and everyone shares and imbibes in blood with one another. What makes Arianna's blood special? Let us, for a moment, take a look at what the PC Hunter encounters should they go to the very depths of the Pthumerian Labyrinth, to the very bottom of Pthumeru Ihyll. It is here that the Hunter fights against the weeping Yharnam, Queen of Pthumeru. But take a closer look at her as you fight her and notice that she seems bound, chained. There is cloth bound around her eyes, blinding her, and her wrists have been tightly chained together to keep her movement restricted. She is restrained for apparently good reason; during the fight with Yharnam she will free herself from her bondage and display a mastery over blood that can only possibly be defined as magic. She melts into blood, using it to travel distances; she uses blood to create false copies of herself, she sprays blood from her fingertips; she stabs herself through the wrists and chest in order to summon blades of blood that swing through the air and impale the Hunter.
Returning back to Arianna, one only needs to take a brief look at her features to see the similarities between her and Queen Yharnam. Where do these similarities come from? From Cainhurst. Arianna’s dress is the dress of a Cainhurst Noblewoman, one like Queen Annalise. Their flowing hair, long sweeping dress, and obvious beauty are all shared. The Noble Dress is found in a Cainhurst portrait room. There are many portraits of Nobles, and one of a tall, crowned woman in a grey dress, holding a blonde child… Perhaps Arianna is a descendant of the Queen Annalise, who had imbibed in Yharnam’s forbidden blood, or if not royalty perhaps she simply has Cainhurst Blood in her genes. Either way, her blood is forbidden. If the PC Hunter has also rescued Adella the Nun in addition to Arianna, they may notice that, when talking to Arianna in the Oedon Chapel, if they angle their camera to the side they can notice that every time they speak to Arianna, Adella will rise from her seat to stare and watch the conversation. When the Hunter finishes speaking to Arianna, Adella will immediately look away and pretend as if she wasn't watching. It's a brilliantly subtle way to show that Adella has her eye on Arianna, and is possibly aware of the blasphemous nature of her blood.
But the similarities between Arianna and Queen Yharnam do not end with their clothing and facial structure. The fate that befell Queen Yharnam would, centuries later, befall Arianna.
Queen Yharnam's childbirth did not go well. Judging from the massive amount of blood staining her stomach and the way she is found weeping in front of Mergo's Loft, we can only assume that the child did not survive the birthing process. When the Blood Moon rises over Yharnam, Arianna first starts to feel pain in her stomach. "Oh… there's something wrong with me." She will refuse to give the PC Hunter any more of her blood, and will have nothing to say until after the Hunter has slain Micolash in the Nightmare of Mensis. If the PC Hunter returns to the Cathedral Ward they will find Arianna's chair empty, and a trail of Serum, clear blood, leading towards the Tomb of Oedon. Following the blood trail we find what is, in my opinion, the most disturbing scene in the entire game: A sobbing Arianna next to a squirming, wriggling Celestial Larva, covered in blood. The implications are… unpleasant. Arianna has gone completely mad, muttering, sobbing, and laughing. "It can't be… this is a nightmare…" The Larva will do nothing but squirm pathetically at her feet until the Hunter kills it. A single attack from any weapon will do the trick. Recovered from the dead creature is an Umbilical Cord: "Every Great One loses its child, and then yearns for a surrogate, and Oedon, the Formless Great One, is no different. To think, it was corrupted blood that began this eldritch liaison."