 The outer frontier was now protected by a wall called the "outer border" (外邊, "wàibiān") that extended from the Yellow River's edge at the Piantou Pass (偏頭關) along the Inner Mongolia border with Shanxi into Hebei province; the "inner border" wall (內邊, "nèibiān") ran southeast from Piantou Pass for some , ending at the Pingxing Pass; a "river wall" (河邊, "hébiān") also ran from the Piantou Pass and followed the Yellow River southwards for about .The Hebei section of the Great Wall was further fortified by planting trees along the wall.As with Yu Zijun's wall in the Ordos, the Mongols shifted their attacks away from the newly strengthened Xuan–Da sector to less well-protected areas.