Being one of the four wholly protected ancient cities in China, Pingyao Ancient City is the"treasure house" of ancient Chinese architecture. With a total length of six kilometers, the city wall is about 12 meters tall and 3 to 6 meters wide on top. The wall is of compacted earth covered by bricks and stones. From a bird's eye view, the rectangular wall resembles a tortoise. There are six city gates on the north, south, east, and west walls. The south entrance is the head of the tortoise. The two wells outside the wall look like the two eyes of a tortoise. The north gate, the lowest place in the city, is the tail of tortoise. Traditionally the tortoise was considered a symbol of longevity, so through ancient times, the hopes were that Pingyao Ancient City would be permanently secure. There are 72 watchtowers on the top of the City Wall and 3,000 external battlements. They represent 72 people of great wisdom, the 3,000 battlements the 3,000 disciples of Confucius.