Barad-dur was the great tower of the Dark Lord Sauron, built deep in Mordor at the foot of the Ash Mountains, and to the north-east of Mount Doom. Barad-dur was constructed in the Second Age of Middle-Earth, and after 600 years of contruction, was finally finished when Sauron completed its foundations with the One Ring. Barad-dur was destroyed when Sauron was defeated by the Last Alliance, but as the One Ring survived, so did the tower's foundation. Barad-dur was rebuilt in the Third Age and Sauron again made it his stronghold, until it was permanently destroyed with the unmaking of the One Ring. Of all the fortresses in Middle-Earth, Barad-dur was the greatest; none who entered ever returned unless Sauron willed it. In the elvish tongue, Barad-dur means "Dark Tower."