The Westmarch was a name used in the Third Age for the region between the Westfarthing and the Tower Hills. It was granted to the Shire by Elessar in SR 1453.

Fastred of Greenholm and Elanor the Fair moved to the Undertowers, on the eastern slopes of the Tower Hills after their wedding. Fastred was then named Warden of Westmarch.

It was in the Undertowers that the Red Book of Westmarch was kept.