The symbolism used in the poem "The Raven" by Edgar Allan Poe is interesting. He uses the bird raven which has an occult or mysterious connotation. In some Native American circles, the Raven is a messenger from the other side. Sometimes, the raven is a messenger of death.
The raven's tapping on the window provides a hypnotic effect coupled with some of the alliteration and onomotopaea. This is a lament about a lost lady-love, the raven is the opposite of the sweetly singing nitingale.
The raven symbolizes the nightmare and depression associated with the loss of love. Other associations of death and decay are the location, the time: midnight, the month: December.