The Wheel of Time - The Call of the Horn
The Blightborder is the northern border of the Westlands, running along the southern edge of the Blight.
Saldaea, Arafel, Shienar, and Kandor share the Blightborder, and are charged with guarding it. This list once included Malkier, though it was overrun by the Blight.
Unlike the Spine to the east, and the ocean to the south and west, the Blightborder is the only unnatural boudary containing the Westlands. It was likely created by the Dark One, though the means of its creation are unknown.