Thamer
A mountain in northern Britain where Uther Pendragon defeated the Saxons Octa and Eosa in his second battle against them.
The battle went poorly for Uther, until he and his warriors, in a small, force, descended upon the Saxon camp in the middle of the night. He captured and imprisoned the two Saxon leaders, temporarily ending the Saxon threat.
Source
Historia Regum Britanniae | Geoffrey of Monmouth, c. 1138