''Threshold'' is a fantasy novel written by Sara Douglass in 1997, and one of the prequels to ''Literature/TheDarkglassMountainTrilogy''.

The story concerns a glassworker slave named Tirzah, forced into slavery because of her father's debts. She's tasked with helping building the eponymous Threshold, a pyramid made partially with huge glass panels. She meets a Magus named Boaz, hiding behind a Magi exterior a little too well. The Magi base a religion and magic power around the One, the number of all creation. And Threshold is being built to allow them to tap into the power of Creation and [[AGodAmI become immortal]].

Once Threshold is completed, though, it... Doesn't go quite as planned.

----
!!Provides Examples Of:

* AntiHero: Boaz.
* BadPowersBadPeople: All of the Magi.
* DeadGuyJunior: Sort of. [[spoiler: Boaz names his and Tirzah's daugher Ysgrave, which was Tirzah's name before she became a slave.]] Tirzah was also named after [[spoiler: Boaz's mother.]]
* DeathByChildbirth: [[spoiler:Neuf]].
* DespairEventHorizon: [[spoiler: One of Nzame's powers is to lock his victims into horror and despair via MindRape.]]
* EarnYourHappyEnding: Everyone has to struggle hard to get their happiness, [[spoiler: especially Boaz, who has to rewrite an ancient spell on the fly and call out to Tirzah to free him on a special night.]]
* EldritchAbomination: [[spoiler: Nzame, a being from the Vale.]]
* EldritchLocation: Threshold is a completely unnatural location.
** [[spoiler: The Vale is an Eldritch world not meant to connect to the human world.]]
* EstablishingCharacterMoment: Boaz's status as a JerkAss is cemented when he destroys Tirzah's masterwork creation simply to spite her. [[spoiler: He gets better.]]
* ExtraOreDinary: Being an Elemental lets you speak to glass and metal.
** [[spoiler: Nzame's]] power turns people into [[HumanoidAbomination stone abominations.]]
* FormulaicMagic: The power of Magi comes from patterns such as math.
* GoneHorriblyRight: Threshold lets the Magi tap into the Vale... only it [[spoiler:summons a demon that starts [[TakenForGranite turning everything to stone]].]]
* HappyEndingOverride: [[spoiler: Darkglass Mountain, as Threshold becomes known, ends up holding much more evil than just Nzame.]]
* HeelFaceTurn: [[spoiler:Boaz, after he finally starts to see just how evil Threshold has become.]]
* HumanoidAbomination: Anyone [[spoiler: Nzame's]] power touches is turned into a stone soldier. Magi are further [[BlessedWithSuck "blessed"]] by [[spoiler: being turned to shrieking glass creatures.]]
* InfantImmortality: Averted. One of the first things Tirzah sees after arriving in Gesholme is a newborn baby having its head splattered against a wall.
* {{Jerkass}}: Chad-Nezzar.
** JerkWithAHeartOfGold: Boaz. [[spoiler: His jerkiness is a defense mechanism created to hide his Cantomancer power from other Magi.]]
* JerkassGod: [[spoiler: Nzame. Subverted, as he is simply a demon pretending to be The One. [[Literature/TheDarkglassMountainTrilogy Not that The One is so kind either.]]]]
* MagicalGesture: The swirling colors required to [[spoiler:speak to the Soulenai]].
* OffscreenMomentOfAwesome: [[spoiler: Boaz enters Threshold entirely on his own, and we never get to see him fight Nzame.]]
* OrderVsChaos: With the Magi representing order and the Elementals representing the chaos of nature.
* {{Precursors}}: Soulenai.
* RapeAndRevenge: [[spoiler:Yaqob stabs Boaz in the stomach for the things he did to Tirzah.]] Also RevengeBeforeReason.
* RapeIsASpecialKindOfEvil: Zigzagged. Tirzah is raped by her slaveholder at the beginning of the book, and she does not carry much resentment for it. However, other characters are incensed when the Magi rape women for their own spiritual enlightenment.
* SecretArt: Elementals and Cantomancers.
* WeaksauceWeakness: [[spoiler: Nzame's]] soldiers are NighInvulnerable. However, they are also so heavy they are incapable of getting up if they are knocked over. This makes them fairly easy to dispatch.
** [[spoiler: Nzame himself]] is unable to leave his pyramid. This makes him easy to approach and deal with once the Cantomancers are ready for [[spoiler: him.]]
* YouCannotGraspTheTrueForm: The Vale, when Tirzah and the others look into it.