Morgai

The Morgai, also known as the Black Fence, was a mountainous ridge in the Ephel Dúath (Mountains of Shadow) which formed a defensive inner wall in Mordor.
Between it and the Ephel Dúath lay a road which ran between Durthang and the Morgul Pass. Frodo Baggins and Samwise Gamgee followed this road north for awhile after the most direct crossing of the Morgai was blocked by a Nazgûl.