 In the west, Shaanxi province became the target of nomads riding west from the Yellow River loop.The westernmost fortress of Ming China, the Jiayu Pass, saw substantial enhancement with walls starting in 1539, and from there border walls were built discontinuously down the Gansu Corridor to Wuwei, where the low earthen wall split into two.The northern section passed through Zhongwei and Yinchuan, where it met the western edge of the Yellow River loop before connecting with the Ordos walls, while the southern section passed through Lanzhou and continued northeast to Dingbian.