"Middle-Earth", or _Endor_, initially describes all the lands between _Aman_ in the West and the _Lands of the Sun_ in the East.

[![Map of Arda after the destruction of the Pillars][1]][1]
<sup>Map of Arda after the destruction of the Pillars, _The Atlas of Middle-Earth_, p. 2</sup>

This particular geography would only last until the Elves are discovered and the Valar fight the Second Great Battle against Melkor. After the battle, "Middle-Earth" is used to refer only to the Northern parts of the continent. The Southern part is called the "Hither Lands" and is rarely referred to.

[![Map of Arda after the Second Great Battle][2]][2]
<sup>Map of Arda after the Second Great Battle, _The Atlas of Middle-Earth_, pp. 4-5</sup>

Note that the _Dark Lands_ appeared after the Second Great Battle, not as part as the destruction of the Lamps.

The next major change in geography is at the end of the First Age, during the War of Wrath, when a large chunk of the Westernmost part of Middle-Earth (_Beleriand_) is completely destroyed and the island of Númenor appears.

[![Map of Arda after the War of Warth, at the beginning of the Second Age][3]][3]
<sup>Map of Arda after the War of Warth, at the beginning of the Second Age, _The Atlas of Middle-Earth_, pp. 38-39</sup>

Finally, near the end of the Second Age, Arda becomes round instead of flat and the island of Númenor is destroyed, but this event does not significantly change the definition of "Middle-Earth".


  [1]: https://i.sstatic.net/i30lK.jpg
  [2]: https://i.sstatic.net/GckQP.jpg
  [3]: https://i.sstatic.net/GsPLp.jpg