Pinnornost (S. "Tree-ridge Fortress") was a border fortress of Anfalas that guarded the path of the Len Lefnui, at the mouth of the Nan-i-Feryth. The fortress was named after its location on the spine of a pine-clad ridge of the White Mountains. The garrison of Pinnornost was under the authority of the Lieutenant-governor of Anfalas at Annúlond and was supplied from the nearby town of Annon Wain. The main task of this garrison was to hold the pass struck by the Len Lefnui between the northern Pinnath Gelin and the outlying ridge of the White Mountains that formed the boundary of the Nan-i-feryth. To facilitate this, Pinnornost was supplied with a beacon tower, which could send signals to a sister tower at the height of the pass, some thirty miles eastward.
Pinnornost was constructed in T.A. 823, following the pacification of Anfalas and the emergence of a frontier zone with the Daen clans of Haerawreigion. It ceased to serve a military function after T A . 2157, when the Lord of Anfalas judged it too costly to maintain a garrison there. Locked up and unused for the remainder of the Third Age, Pinnornost gradually fell into disrepair. It was not reinhabited during the reign of Aragorn Elessar.