Barad-dûr is the fortress where Sauron resides in J.R.R. Tolkien’s Mordor.
The name Barad-dûr means “Dark Fortress” in Tolkien’s constructed Sindarin language. Sauron builds it in Mordor during the Second Age, using the power of the One Ring to strengthen its foundations. It becomes the central stronghold from which he dominates the surrounding land and commands his armies.
After Sauron’s defeat at the end of the Second Age, Barad-dûr is destroyed. Sauron later rebuilds it during the Third Age, and it stands as the most visible symbol of his renewed power in The Lord of the Rings. The fortress is linked to the volcanic Mount Doom, where the One Ring was forged and must ultimately be destroyed.
Barad-dûr is often confused with Orthanc, the tower of Isengard, or Minas Morgul, the former Minas Ithil. Those places are important strongholds, but neither is Sauron’s main residence in Mordor.