why is the forbidden city unique and special?

In my opinion, there are three reasons.
1. It is the heart of Beijing and the most complete imperial palace in China. About 24 emperors in Ming and Qing Dynasties lived there in hundred years. It has a long history.
2. Specail efforts are made to construct it. Every place is constructed according to Chinese culture and every kind of material was hard to get at that time.
3. It fully embodies artistic features and style of ancient Chinese palace architecture.