Great God Pan, The by Arthur Machen (1863 - 1947)

with another story, "The Inmost Light") in 1894. On publication it was widely denounced by the press as degenerate and horrific because of its decadent style and sexual content, although it has since garnered a reputation as a classic of horror. Machen’s story was only one of many at the time to focus on Pan as a useful symbol for the power of nature and paganism. The title was taken from the poem "A Musical Instrument" published in 1862 by Elizabeth Barrett Browning, in which the first line of every stanza ends "... the great god Pan."
(via Wikipedia)