Fill in the blanks according to the requirements, and talk about your understanding of Zhao Zhouqiao's "This design is a pioneering work in the history of bridge architecture".

There is no pier under Zhao Zhouqiao, only an arched bridge opening. On the left and right sides of the ceiling of the bridge, there are also two small arched bridge opening. At ordinary times, the river flows through bridge opening. When there is a flood, the river can also flow through four Kobashiguchi. This reduces the impact of running water on the bridge, reduces the weight of the bridge and saves stone.