[P 011&P013 / Jiayuguan] was first established in 1372 as a simple enclosure surrounded by earthen walls. In 1495, a western gate tower was added, and in 1506/7 an eastern gate tower. In 1539, the walls were doubled in height to the 30 or so feet that they are today. Pounded earth was used as a foundation and brick added.
Long walls were also built for added security in the area - three in total. The first two - the 10-mile western wall and the 24-mile eastern wall - were constructed between 1539 and 1541, and the third - the 10-mile northern wall - in 1573. The northern wall connects to other border walls. Walls were also built west of the Yellow River in the 15th and 16th centuries. A 27-mile-long stretch of the 1531 Xiguanmen Wall can be seen today at Sanguankou.
