Where does the great A' Tuin come from?

I've been wondering where the inspiration/idea for the Disc being supported on the backs of elephants standing atop a turtle swimming through space.

I've come across a couple of passages and quotes from the non-discworld world, that I'm pretty sure are not related. For instances Richard Feynman uses a his value of science lecture, it is possible that he got this from Pratchett I really don't know. I'm wondering if there is larger mythological connection that I'm not aware of?

I'm not saying this is the answer, as I haven't heard what Pratchett has to say on the subject, but the idea of a world on a turtle's back is not new. Here is an Iroquois Creation story which has that premise.

http://www.cs.williams.edu/~lindsey/myths/myths_12.html

And this is a quote from the great Wikipedia
"In the cosmological myths of several cultures a World Turtle carries the world upon its back or supports the heavens. The mytheme of a World-Tortoise, besides that of a world-bearing elephant, was discussed by comparatively by Edward Burnett Tylor (1878:341)."

In "The Discworld Companion" Sir Terry himself answers your question.

p. 7:

...we seem to have a turtle-shaped hole in our consciousness. On every continent where turtles grow, early man looked at the things sunning themselves on a log...and somehow formed the idea that a large version of one of those carries his world on its back.

p. 8:

I came across the myth in some astronomy book when I was about nine. In those white-heat-of-technology days every astronomy book had an early chapter which was invisibly entitled "Let's have a good laugh at the beliefs of those old farts in togas"...And there was the Discworld, more or less. The image remained with me...and trotted forward for inspection much later when I needed it.

Much shortened by me.

Funny how I've never come across a creation myth with turtle before, just the quotes of a myth. Thanks for yall's informative answers.

I am currently reading a book called Oriental Rugs; a Buyer's Guide and I have just read about the Herati design.

I Quote: "It is sometimes referred to as the mahi or 'fish-in-the-pond' design (mahi being the Persian word for fish), because many traditional sources have cited this as its symbolic origin. In Persian mythology the world was supported by four swimming fish."

It occurred to me that this might have contributed to The Great A'Tuin swimming through space with the four elephants supporting the Discworld.

Fish? That's rubbish, it's turtles all the way down! ;)