Non-Canon Alert! The subject of this article originates from non-canonical sources. To find out about what is considered "canon" see LOTR:Canon.
The Mithram Spur were the mountains stretching across north-eastern Mordor east of the plains around Barad-dûr. On the Mithram Spur were other fortresses in Mordor such as Seregost, and there were a few valleys through which the Dark Lord could see the movement of his armies in Lithlad.
Across the gap at the spur's tip, to the west, was the Maegond Spur.