Poe creates an atmosphere of horror in "The Pit and the Pendulum" by keeping the reader constantly in suspense and uncertainty. Readers are plunged abruptly into the action from the first sentence, without any explanations. The narrator is sick, but it is unclear why. They unbind him and permit him to sit, but we do not know who "they" are. He is sentenced to death, but his crime is undisclosed. These uncertainties are all contained in the first few lines, creating a feeling that anything could happen.

This technique continues throughout the story. The narrator's cell is so profoundly dark that anything could be lurking within it. His mind is tormented with fables and images "too ghastly to repeat." It takes him quite some time to discover the pit while he continually reflects on all the horrible ways in which he might die. When he later faces death from the pendulum, the huge rats which deliver him from his plight are even more physically disgusting than the prospect of death from the swinging scimitar. Even his salvation, therefore, contributes to the atmosphere of horror:

They pressed—they swarmed upon me in ever accumulating heaps. They writhed upon my throat; their cold lips sought my own; I was half stifled by their thronging pressure; disgust, for which the world has no name, swelled my bosom, and chilled, with a heavy clamminess, my heart.

The narrator's rescue by General Lasalle brings a sudden end to the story. This means that the nightmarish atmosphere of uncertainty and terror persists until the last few lines. Until then, readers feels that a terrible death might overtake the narrator at any time, preserving the atmosphere of horror until the last possible moment.

How does Poe create suspense in "The Pit and the Pendulum"?

One way that Poe creates suspense from the very beginning is by giving us an unreliable narrator to narrate the events. He opens the narrative by telling us that he himself doesn't fully trust his senses:

I was sick—sick unto death with that long agony; and when they at length unbound me, and I was permitted to sit, I felt that my senses were leaving me.

If the narrator himself doesn't feel that he has full control of his senses and faculties, how can we be sure of the details that follow? How will he portray the events?

Suspense is further generated by the setting. Part of the narrator's torture is that his punishment is hidden in darkness:

At length, with a wild desperation at heart, I quickly unclosed my eyes. My worst thoughts, then, were confirmed. The blackness of eternal night encompassed me. I struggled for breath. The intensity of the darkness seemed to oppress and stifle me. The atmosphere was intolerably close.

The unknown terrors that lay waiting for the narrator in the darkness increase his sense of panic, and therefore, the reader's as well. Darkness is often symbolic of evil, and this sense of foreboding danger intensifies as the narrator attempts to navigate his dark surroundings.

Thus, the narrator's reaction to his torture increases suspense. Perspiration bursts from every pore. His eyes strain for hope. He thrusts his arms wildly in all directions.

And then, of course, there is the method of torture itself. A swinging pendulum that ends in a sharp blade which descends ever closer to the narrator, with potentially disastrous results, creates a building sense of terror. The pendulum descends slowly, allowing the narrator much time to consider his gruesome end and time for the reader's anticipation to build, as well.

Poe masterfully crafts a language that furthers an eerie tone, utilizing words such as "relentlessly," "unspeakable," "devoured," "struggled," and "annihilated"—and weaving this language throughout the story to increase the story's suspense.

How does Poe create suspense in "The Pit and the Pendulum"?

Edgar Allen Poe was the first writer to use many horrific archetypes, or universal themes or mental images, in his stories. To create suspense in "The Pit and the Pendulum," he uses numerous archetypes that inspire a sense of terror, including helpless captivity, darkness, torture, rats, imminent death, and a deep almost bottomless pit.

To further heighten the suspense, Poe creates an acutely sinister atmosphere and draws out the narrator's encounters with each of these fearful things. For instance, when the narrator's sentence is pronounced, he is in a candle-lit room faced by black-robed judges, and the narrator is "sick unto death with that long agony" of not knowing his fate and fearing the worst. When he awakens in utter darkness, Poe draws out the feeling of horror by having him measure the length of his dungeon, and then increases the suspense by having him almost fall into the pit. When he is bound to the wooden framework and the pendulum descends, it inches its way down in agonizing slowness, further creating suspense. Finally, when the narrator escapes the pendulum, he is not simply cast into the pit, but is slowly, slowly forced towards it by the hot enclosing walls.

So Poe creates suspense by using what are now considered classic horror archetypes, by his description of the terrible environment of the dungeon, and by drawing out the narrator's danger by various means with intense, excruciating slowness.

How does Poe create suspense in "The Pit and the Pendulum"?

Poe creates suspense, in part, by using a first person narrator. This means that the narrator is a participant in the action and that he uses the first person pronoun, "I." The first person narrator can really only tell us what he's aware of and what he knows to be true, as opposed to a third person narrator who might be able to tell us what all the other characters are thinking and feeling. Because the narrator's perception is limited by darkness and his experience is limited by solitude, he can only tells us as much as he knows, and that is not too much. This creates suspense. Further, the narrator loses consciousness more than once, and we are as clueless as he is as to what he will find when he awakens. Moreover, the narrator talks about being in Toledo, and given his trial, judgment, and torture, we might ascertain that he is being held by the Spanish Inquisition, and this would create suspense as well because we know how ruinous and deadly it was.

How does Poe create suspense in "The Pit and the Pendulum"?

I think that a big part of the suspense in "The Pit and Pendulum" comes from two sources.  

The first is the unknown. The reader has no idea why the protagonist has been arrested and sentenced. The opening paragraphs have him in and out of conscious thought all while hallucinating. We don't know who he is or what he has done to deserve punishment. Once he is in his cell, the unknown continues. It's too dark to see anything, so the protagonist (and reader) has no idea where he is. After he successfully evades the pit, the protagonist must face the pendulum. There is always a sense of "what could possibly come next?" That's suspenseful reading.  

The second source for suspense is the protagonist's solitude. Being alone in an unknown place is scary. Having to suffer alone is scary. If the narrator had a cellmate, then readers might hope the two could at least help each other cope. That isn't an option for the protagonist, though. He must go about his torture alone. He's only dependent on himself, which I believe makes the story more suspenseful.

How does Poe create atmosphere and tension in "The Pit and the Pendulum"?

Poe was a master at creating spooky and suspenseful moods in stories. In "The Pit and The Pendulum," his narrator is subjected to gruesome torture during the Spanish Inquisition.

Poe toys with the narrators senses, creating a dream-like state of the narrator's judgement. The judges sound like a "dreamy hum," and then fade out, and shapes of candles appear as angels and become unclear again, and everything disappears into darkness. The narrator awakens into pitch black darkness, and fades in and out several times throughout the story. By telling the story through this narrator, the reader feels as though they, too, are moving in and out of consciousness.

When he next awakens into light, there are terrible images, and most prominent, an image of Father Time holding a razor sharp pendulum that is getting closer and closer. Poe toys with the ideas of light and dark, and creates a swinging pendulum to count down the time that the narrator has left.

The use of these sensory shifts and the description of the terrifying images, tiny suffocating space, the counting down of the swinging pendulum, and the closing of the walls all lend to the tense, horrifying atmosphere of the story.