Celydonn is the setting of two {{fantasy}} trilogies by TeresaEdgerton: the Green Lion Trilogy and the Celydonn trilogy. It can be thought of as an AlternateUniverse mediaeval Britain in which magic is real, but it isn't a straight AlternateHistory setting.

For example, the setting as introduced in ''Child of Saturn'' has recognizable analogues to various figures of the KingArthur legend - the kingmaker wizard Glastyn, the High King and his queen, the knights of the king's Order of St. Mark - but with significant changes to the characters and a different culture and history.

The Green Lion Trilogy consists of:
* ''Child of Saturn''
* ''The Moon in Hiding''
* ''The Work of the Sun''

The titles of the Green Lion trilogy (including that of the trilogy itself) are references to alchemy. (The king's wizard, who is the female protagonist, is an alchemist, as was her predecessor. They both pursue alchemy not for the sake of becoming rich, since it's simply not cost effective, but for how it tries and purifies the one who seeks wisdom by its study.)

The Celydonn trilogy, a sequel trilogy to the Green Lion trilogy, focusing on a different subset of the original trilogy's cast, consists of:
* ''The Castle of the Silver Wheel''
* ''The Grail and the Ring''
* ''The Moon and the Thorn''

This series provides examples of:
* AlienSky: In ''The Grail and the Ring'', the Inner Celydonn's version of Tir Gwyngelli currently has three moons. Its neighbours have differing numbers of moons.
* AltarTheSpeed
* AlternateUniverse: the Inner Celydonn
* ArrangedMarriage
* ArtifactOfDoom: the titular grail in ''The Grail and the Ring''
* BiggerOnTheInside
* {{Bizarrchitecture}}
* CannotTellALie: one of Prince Tryffin's geasa, along with things such as 'never take iron from the dead'.
* ChessWithDeath
* ChildhoodMarriagePromise: subverted in ''The Castle of the Silver Wheel''
* {{Curse}}
* EvilMentor
* TheFairFolk
* FullBoarAction
* FunctionalMagic
* InnocentCohabitation
* TheJailBaitWait
* KingArthur: the names are changed, however, and the personal relationships play out very differently - the queen is faithful to her husband, and has better sense than he does about some things.
* TheKingdom
* KissingCousins
* KnightInShiningArmor
* LaserGuidedAmnesia
* MadScientistLaboratory
* MistakenForCheating
* OlderThanTheyLook
* OurWerewolvesAreDifferent
* PlotCoupon: the titular grail from ''The Grail and the Ring''
* ProphecyTwist
* RelationshipUpgrade
* ReligionOfEvil: the Black Canons ([[spoiler:the villains formerly known as the cult of Cerridwen]])
* RoyalBrat: Calchas
* RightfulKingReturns: [[spoiler:Mahaffy]] turns out to be this in the second trilogy.
* RoyalBlood
* RoyallyScrewedUp: the Lords of Mochdreff
* SetRightWhatOnceWentWrong: the main plot of ''The Grail and the Ring''
* SpeakNowOrForeverHoldYourPeace
* StandardRoyalCourt
* TimeTravel
* TrialByCombat: Discussed
* TheUnfavourite
* VisionsOfAnotherSelf
* TheWatcher: Dame Ceinwen
* WeddingDeadline
* TheWisePrince: Tryffin, in the second trilogy.
* ZombieApocalypse
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