Bem, vou colocar o que achei na "Tolkien Illustrated Encyclopaedia", mas vou colocar em inglês mesmo pq não tô com saco de traduzir (tô com um pouco de sono pra isso). Isso se encontra na parte onde o autor descreve a geografia da Middle-earth.
Mordor - At the end of the first millennium of the Second Age, Sauron founded an evil kingdom on Middle-earth, just to the east of the River Anduin. This was called Mordor, the “black land”, and for two ages was Sauron´s base of power in his quest for dominion over all Middle-earth. Mordor was defended on three sides by two unassailable mountains rages: the Ash Mountains in the north, and the Sahdowy Mountains in the west and south. Through these mountains, there appear to have been only two passes: Cirith Ungol in the west and Cirith Gorgor in the northwest. Besides the small circular plain called Udûn inside Cirith Gorgor, Mordor´s two major regions were the Plateau of Gorgoroth and the slave fields of Nurn. Gorgoroth was a vast dreary plateau of slag heaps and Orc pits always under the pall of smoke from the volcanic mountain of Orodruin (or Mount Doom) near its center. Here too, on the northeast side of the plateau on a spur of the Ash Mountains, was the Sauron´s stronghold, the Dark Tower of Barag-dûr. Nurn, however, was a vast farmland populated by slaves and slave-drivers who supplied the massive foods and basic materials for Sauron´s armies. Nurn was drained by four rivers, and each flowed into the inland sea of Nûrnen. After forging the Rings of Power and the One Ring in the fires of Mount Doom in 1600, Sauron completed Barad-dûr and began the War of Sauron and the Elves. Although surrendering to the astonishing power of the Númenóreans in 3262, Sauron managed to destroy them by guile and return to Mordor after Númenor´s destruction. In 3429, Sauron´s forces made war on Gondor, but retribution came in 3434 when the Last Alliance of Elves and Men destroyed his army on Dargolard and broke down the Black Gate in order to enter Mordor. After a seven-year siege Barad-dûr was taken, the One Ring was cut from Sauron´s hand, and all of his evil servants driven out of Mordor. During the early part of the Third Age, Mordor was empty and Gondor built the Tower of the Teeth and the fortress of Durthang in the north pass, and the Tower of Cirith Ungol in the west pass, to watch over Mordor and prevent any of Sauron´s scatted allies from entering the kingdom. Unfortunately, after the devastation of the Great Plague of 1636, Gondor abandoned these fortresses and they were taken over by Orcs and prepared for the entry of the Nazgûl and Sauron himself. In 2942 Sauron returned and in 2951 began rebuilding Barad-dûr. However, the unmaking of the One Ring proved a final blow. Sauron was destroyed for the last time and Mordor was never again a threat to the peace of Middle-earth.
