Klingon-Romulan border
From Memory Alpha, the free Star Trek reference.
The Klingon-Romulan border was the division between the Klingon Empire and the Romulan Star Empire.
Khitomer was located near the border on the Klingon side. (Star Trek VI: The Undiscovered Country)
In early 2372, the Klingon Empire attacked several Romulan outposts along the border. (DS9: "Hippocratic Oath")
