Where is Middle-earth and is it flat or curved?

Question

After seeing this article about what Middle-earth would look like from space, and reading one of the first comments, which indicates that there are hints that Middle-earth is flat, I'm left with what seems to be an obvious question:

Where is Middle-earth? And is it flat?

Is Middle-earth supposed to be on Earth sometime before recorded history, or on islands or continents that were lost due to the motion of tectonic plates? Is it supposed to be in a mis-shapen Europe during the historical period that would match the development in Middle-earth?

Or is it supposed to be on a different planet or location entirely? And if so, what are the indications that it is flat? (And is it flat or curved?)

Answer 1

Middle-earth is supposed to be our own world in a distant legendary past--see this page for some quotes by Tolkien on the subject. For example, he's quoted saying:

"The action of the story takes place in the North-West of ‘Middle-earth’, equivalent in latitude to the coastlands of Europe and the north shores of the Mediterranean (…) If Hobbiton and Rivendell are taken (as intended) to be about the latitude of Oxford, then Minas Tirith, 600 miles south, is at about the latitude of Florence. The Mouths of Anduin and the ancient city of Pelargir are at about the latitude of ancient Troy."

But then he's also quoted saying "Those days, the Third Age of Middle-earth, are now long past, and the shape of all lands has been changed…", suggesting that any mapping to present-day lands wouldn't be exact. This page also has some more relevant quotes from Tolkien, including the following:

"'Middle-earth', by the way, is not a name of a never-never land without relation to the world we live in .... And though I have not attempted to relate the shape of the mountains and land-masses to what geologists may say or surmise about the nearer past, imaginatively this 'history' is supposed to take place in a period of the actual Old World of this planet."

Answer 2

In Akallabêth, it is documented that "Illuvatar showed forth his power, and he changed the fashion of the world". In the First and Second Ages, the world had been flat. At end of the Second Age, the seas were bent and the world made curved. Valinor, the Undying Lands that the ringbearers travel to at the end of the Third Age, does not follow this curvature and only the elven ships can travel along the original 'straight' path beyond this curvature.

Answer 3

Middle-earth was described by Tolkien as "Europe at some time in its prehistory". I'm not an expert in that subject, but I can elaborate on the issue of the shape of the world.

Middle-earth is located within the greater domain of Arda, which includes other continents. Originally, the domain of Arda was flat, with Middle-earth located roughly in its center. Between Middle-earth and the Undying Lands to the west was the island of Numenor, whose inhabitants were blessed in that they could see the edge of the Undying Lands from their home. In order to punish the Numenorians for their pride, their island was sunk and in the process the world was made round. This all occurred thousands of years before the events of the Lord of the Rings, so Arda is round during the books.

Answer 4

In the Silmarillion it is said that the Middle-earth or better the whole world was flat, when Eru Iluvatar created it. After the long crysis with the Melkor (ancient master of Sauron, which was but a shadow to Melkor) Eru has made his first and last appereance in the world to banish Melkor and to curve the World and lift the heavenly cities of High Elves in the West. After that no normal ship could reach High Elven homes in the West where also other dieties (Valar and Maiar) dwelled. If you would sail west you would get back to the beginning.