Introduction to Nantianmen: According to historical records, these castle-like buildings were built by the Chu State during the Spring and Autumn Period and the Warring States Period to prevent the invasion of other countries. They are all made of stones. According to research, they are the father of the Great Wall of China. The ruins of the "Chu Great Wall" are nearly 400 years older than the Qin Great Wall. Now these castles are being restored according to their remaining features.