Specialize

There is in fact another bit of history related to the specialization of queen and bishops as the pieces for defence in the Chinese chess.

For over one thousand years in the history of China since the Warring States Period (戰國時代), government officials were not classified into administrative (文官) and military (武官) groups. To be specific, there were positions for either, but officials simply took turn on a somewhat rotation basis - obviously depending on the actual need of the empire at that moment. Therefore you could find Zhou Bo (周勃), Zhuge Liang (諸葛亮), Li Jing (李靖) and many others taking up the position of an army general at one time and the prime minister at another.

This is what was known as "出將入相".

The system, however, was abolished in the middle of the Tang (唐) dynasty.

To be specific, this rotation program was banned by the famous (for being malicious !) prime minister, Li Linfu (李林甫). Yes, the one who was well known for the honey in his mouth and dagger in his heart (口蜜腹劍).

(Rumours said that he banned the system because he was so much a coward that he could not stand leading an army. That's for sure the romantic idea of some naive Chinese historians. The more likely reason was he could not afford the risk of his position as the prime minister being taken up by others - who might discover how his sweat mouth ate up a large part of the government expenditure !)

Well, whatever the cause was, from the very point onwards, the central government lost touch with the army leaders at the front line - the latter was inevitably forced either to die of negligence or to rise in rebellion.

PS. In the Tang era, Chinese chess board had no river or palace, and every piece could go around just like the international chess nowadays. The "modern" chess board appeared in the Sung (宋) dynasty - when the rotation system had long been forgotten.