The name Barad-dûr is Sindarin, from barad “tower” and dûr “dark”. It was called Lugbúrz in the Black Speech of Mordor, from lug “tower” and búrz “dark”. The Black Speech (created by Sauron) was one of the languages used in Barad-dûr. The soldiers there used a debased form of the tongue. In The Lord of the Rings “Barad-dûr,” “Lugbúrz,” and “the Dark Tower” are occasionally used as metonyms for Sauron.

In the Second Age, Sauron began to stir again and chose Mordor as a stronghold in which to build his fortress. It was strengthened by the power of the One Ring, which had recently been forged; its foundations would survive as long as the Ring existed. Gandalf described the Ring as being the “…foundation of Barad-dûr…” The Dark Tower is described as being composed of iron, being black and having battlements and gates. In a painting by Tolkien, however, the walls are of mainly grey stone and brick, and battlements, gates and towers are not visible.