Barad-dûr was the tower fortress where Sauron lived in Mordor in J.R.R. Tolkien’s books.
The name Barad-dûr is Sindarin and means “Dark Fortress.” Sauron built it in Mordor during the Second Age, using the power of the One Ring to strengthen its foundations. The fortress stood near Mount Doom and served as the center of Sauron’s power.
Barad-dûr was destroyed when the One Ring was destroyed in the fires of Mount Doom. Tolkien describes it collapsing as Sauron’s power failed, bringing down the main symbol of his dominion over Mordor.
Orthanc is a different tower, located in Isengard and associated with Saruman. Minas Morgul is the former Minas Ithil, while Dol Guldur is a fortress in southern Mirkwood, so these names are frequent sources of confusion.