Why is that wall outside the ancient government building?

That wall is called the shadow wall, which is not only owned by the government, but also by the mansion doors of rich people. It is the characteristic of Ming and Qing architecture. Its first function is to shield privacy when the main entrance is open and prevent outsiders from seeing the situation in the yard. Second, it embodies majesty and dignity. Many screens have inscriptions by dignitaries, calligraphers and even emperors.