How did Poe affect the Romantic Period?

Edgar Allen Poe was one of the most influential and prolific writers of the Romantic Period. The Romantics were reacting against the Enlightenment, which was a literary (among other things) movement concentrating on rationality and reason as the most valuable tool for humans to understand the world. The Romantics, on the other hand, rejected the notion that everything could be understood with the mind, and preferred to write about the supernatural and irrational. They were more attracted to the animal, emotional side of humans and the dark, unknowable side of the universe. Horror became very popular, as well as dark fantasy.
That said, Edgar Allen Poe's writing is one of the most perfect examples of this ethos. "The Cask of Amontillado" is a tale of irrational revenge—the protagonist is seeking to murder a man for a perceived insult. Likewise, the exploration of terror in "The Pit and the Pendulum" is a good example of Poe showing how the human mind is not a perfectly rational machine. In general, Poe's explorations of madness are exemplify the Romantic period, because showing how human rationality can fail was a primary goal of the movement. Finally, in poems like "The Raven" and "Annabel Lee," the concept of mourning for a lost lover is an expression of grief and despair that is typical of the Romantics—they were intrigued by death and loss, in opposition to the Enlightenment, which tried to be constructive and positive.