There are a number of particularly bizarre things about Terry Pratchett's reading Discworld in order requires a flow chart, or at least a willingness to leap into a book with little to no context.

Yet possibly the strangest part of the Disc (or at least the part that, when explained to the uninitiated, often leaves them with a bemused expression) is its physical makeup. The Disc is a world precariously and inexplicably balanced on the back of a turtle flying through space – a fact that most of the Disc's inhabitants, or at least the ones who are aware of it, consider perfectly normal. Those few who are aware of our own world, which they call Roundworld, think we're the weird ones – and in a way, we really are.

Who Is Great A'Tuin? Discworld's Turtle & Setting Explained

No One Knows The Great World Turtle's Origin Or Destination; We Only Know That The Turtle Moves

The Discworld's name comes from its literal disc shape; the Disc is approximately 10,000 miles across, with a thickness of 30 miles at the Rim that increases steadily towards its center, called the Hub, from which the plateau of the Hublands and the great mountain Cori Celesti jut above the rest of the world. Rotating clockwise at a languid speed of one full rotation every 800 days, the Disc is balanced atop four gigantic elephants – Berilia, Tubul, Great T'Phon, and Jerakeen – who are themselves balanced atop the shell of the mighty turtle A'Tuin.

Extensive subterranean deposits of eldritch fat in the kingdom of Uberwald imply that, in prehistoric times, a fifth elephant also helped the Disc, although the nature of how it crashed into the Disc remains unknown.

Great A'Tuin, as the Disc's residents call it, is a starfaring turtle of a species known as Chelys galactica, which roam the cosmos; in the novel Pyramids, A'Tuin is described as "the only turtle to ever feature on the Hertzprung-Russel diagram," which is how astronomers graph a star's temperature and luminosity. The particulars of A'Tuin's method of reproduction – and even the mighty turtle's sex – remain a mystery to the scholars of the Disc, although the end of the second novel, The Light Fantastic, shows A'Tuin shepherding eight newly-hatched Chelys galactica (each with its own tiny Disc) out into deep space.

Discworld Resting On A Turtle Draws From Hindu Mythology

Great A'Tuin, As With The Rest Of The Disc, Is A Funhouse Mirror In Which We See Our Own Reflections

The idea of the world resting on the back of a giant turtle is not an original creation of Terry Pratchett; the most prominent manifestation of that concept in real-world stories is Akūpūra, the World Turtle of Hindu belief, who is an avatar of the ultimate preserver deity, Vishnu. Hindu myth also has the Ashtadiggajas and the Ashtadikkarinis, eight male and eight female elephants who serve as divine guardians of the corners of the world.

There is inconsistent scholarship about whether the elephants also stand on the shell of the World Turtle to hold up the world, or if that function is performed by a snake, as the original texts use the Sanskrit word "Nāga," which can mean either; initial English-language records of myths related from Indians to Europeans tend to be wildly inaccurate, if not outright racist, and rarely bothered with such things as asking for clarification.

Other cultures throughout history have also had World Turtles of their own. Chinese folk legends, which carried over into Chinese Buddhism, Confucianism, and Taoism, tell of how the mother goddess Nüwa mended the Pillar of Heaven by using the four legs of the great turtle Ao to hold up the sky. A creation myth common to multiple North American Indigenous people, including the Lenape and Haudenosaunee (more commonly known as the Iroquois, although that name was imposed on them by the French and other colonizers), states that the world, atop a great turtle, floats amid a massive sea.

Discworld's Setting Perfectly Fits With The Books' Themes

If The Disc's Topography Wasn't Bizarre, The Stories Told There Wouldn't Be Half As Interesting

While Pratchett clearly drew from multiple mythologies when he created the Discworld, particularly the Hindu form of the World Turtle, he also imbued the world with a generous helping of his signature blend of satire and philosophy. According to the Disc's greatest scientific minds – the wizards of the Unseen University in Ankh-Morpork – A'Tuin and the elephants are all made of concentrated narrativium, an essential element of the Disc's universe that allows its base natural law of Narrative Causality to function. To quote a poignant Pratchett age from Witches Abroad:

Stories, great flapping ribbons of shaped space-time, have been blowing and uncoiling around the universe since the beginning of time. And they have evolved. The weakest have died and the strongest have survived and they have grown fat on the retelling… stories, twisting and blowing through the darkness.

And their very existence overlays a faint but insistent pattern on the chaos that is history. Stories etch grooves deep enough for people to follow in the same way that water follows certain paths down a mountainside. And every time fresh actors tread the path of the story, the groove runs deeper.

This is called the theory of narrative causality and it means that a story, once started, takes a shape. It picks up all the vibrations of all the other workings of that story that have ever been. This is why history keeps on repeating all the time.

All of that means that on the Discworld, stories happen because they must. Dragons breathe fire because, in stories, dragons always breathe fire, and a million-to-one chance for a hero to succeed tends to work out in their favor about 90% of the time. Therefore, it's only logical that the Disc sits on the back of a World Turtle – humans in our world have been telling that story for thousands of years. It's the same bizarre logic that permeates all of Terry Pratchett's writing and ensures that the best Discworld books will be adored by storytellers for generations to come.