: Estimated at approximately 1,500 meters (4,921 feet).

: A "mountain of iron" with wall upon wall and battlement upon battlement.

: Built with "adamant" and featuring iron crowns and steel gates.

Tolkien described the fortress as a massive, near-indestructible structure:

Barad-dûr was built by Sauron in the land of Mordor, not far ... - Facebook

: Its existence was bound to the One Ring ; the foundations were laid using the Ring's power, making them unshakable while the Ring remained. Role and Purpose