At the time when Zhu Yuanzhang captured Huizhou, long be fore the establishment of the Ming Dynasty, he was astonished by a hermit named Zhu Sheng, who told him to "build high walls, store abundant provisions and take your time in proclaiming yourself emperor", advice which Zhu Yuanzhang heeded.

Once the whole country was unified, he sent orders to the local governments to build city walls on a large scale. Zhu assumed that "out of all the mountains and rivers in the world, the central Qin is the most strongly fortified and strategically impregnable. The city wall of Xi'an is an extension of the old Tang Dynsty structure, as a reslt of this wall building campaign.

A watch tower is located on each of the four corners of the wall. The one at the southwestern corner is round, probably after the model of the imperial city wall of the Tang Dynasty, but the other three are square-shaped.

The first city wall of Xl'an was built of earth, rammed layer upon layer. The base layer was made of earth, quick lime, and glutinous rice extract, tempered together. It made the wall ex- tremdy strong and firm. Later, the wall was totally enclosed with bricks. On top of the wall, there is a brick water trough every 40 --60 metres, they are used for drainage. They have played a very important role in the long-term protection of the city wall of Xi'an.