One of the major aspects of steampunk comes from its dystopian elements. The Difference Engine by William Gibson and Bruce Sterling weaves in dystopic facets, as does Boneshaker by Cherie Priest. Though the first dystopian story is generally accepted to be After London, or Wild England by Richard Jeffries (1885), the influence of Gothic Literature, and particularly Urban Gothic, cannot be understated.
Gothic literature can be tied to the Gothic Revival movement in architecture of the same time period. The writers of Gothic literature focused on extremity of emotion and the creation of Atmosphere (yes, the capital A is important), in addition to the general theme that man's works would not last forever. The focus of the Gothic Romances that came about in the late 18th and early 19th centuries was thus the the creation of this dark and terrifying world through psychological and physical terror.
Prominent stories from this period include Mary Shelley's Frankenstein (1818), The Castle of Otranto by Howard Walpole (1764), and The Old English Baron by Clara Reeve (1778). One of Jane Austen's works, Northanger Abbey, is valuable because it references a series of novels now nicknamed the Northanger Horrid Novels. There was a timeframe where Gothic writers, specifically Ann Radcliffe, were seen as composing sensationalistic women's entertainment (sounds like the bad rap romance novels get today, huh?).
This is the genre that birthed the Byronic hero, a man who is "mad, bad, and dangerous to know," and yet is seen as a heroic figure in spite of that. This strikes me as a forerunner of the Anti-Hero trope that is so common in modern fiction.
Tales like Frankenstein, and the Victorian Gothic stories of Edgar Allen Poe and others gifted us with the dark, brooding aesthetic of later horror novels and the extremity of emotion needed in the darker steampunk works. Oscar Wilde's The Picture of Dorian Grey offers fodder for dark discussion about beauty and Faustian deals with the best of them. The story is chilling in one of the best sorts of ways, and forces you to think about how far you're willing to go to protect the things that matter to you.
Darkness and terror characterize the great Gothic stories of the Victorian period, something any author interested in the darkness of humanity can learn a lot from.
Thursday: Mary Shelley's Frankenstein; or, The Modern Prometheus*
* Tomorrow is Secret Archives day.