One theory is that the southwest corner is located in the earthquake zone. As long as the corner platform is square, there will be problems. In the end, there is nothing to do but keep the circle.
Another way of saying it is that since Zhu Yuanzhang accepted the suggestion of "building a wall high, accumulating grain widely, and slowing down to be king", he deeply felt that "it is not safe to hide inside and store outside". Therefore, counselors Liu Ji and Yao presided over the design of the city and showed the world how to build it.
After Liu Ji and Yao were appointed, they discussed and revised many times, and finally drew a rectangular pattern in the traditional form. Unexpectedly, Zhu Yuanzhang felt uncomfortable after reading it, saying, "Although there are certain rules for building a city from ancient times to the present, according to my experience, it is not appropriate to stick to the rules. The Book of Rites says, "Try to make rules and don't bully Fiona Fang". I think it is better to change it. "
After that, he lifted the pen and erased a corner of the rectangular pattern. Thus, the urban schema changed by the emperor's imperial edict was presented to the world. It is said that most cities built in the Ming Dynasty follow this formula.
There is another saying that when planning the Xi 'an city wall, all four corners were right angles, but later, when dealing with the foundation of the city wall, the ancient Tang Cheng site was accidentally discovered in the southwest corner. The site is semi-circular, and the original foundation is used conveniently in order to save time and labor.
This statement sounds reasonable, but if we take the buildings of the Tang Dynasty such as Little Wild Goose Pagoda as coordinates, combined with the size of Chang 'an Square and the width of the street, we can draw the conclusion that Xi 'an Chang 'an City has nothing to do with the location of Chang 'an City in the Tang Dynasty.
There is also a saying that the traditional architecture in China is influenced by the requirements of gossip and geomantic omen, so the architecture should not be too symmetrical. Such as yamen, temples and residential buildings, the front door must not be symmetrical with the back door, and the longitudinal axes of the front and rear doors must be staggered by a certain distance. It is this "asymmetry" that requires architecture, which determines that one of the four corners of Xi 'an city wall must not be a right angle.