Why did Zhang Zeduan regard the bridge as the climax of the picture in The Riverside Scene at Qingming Festival?

The water under the bridge and the pedestrians on the bridge, one moving silently and the other moving silently, reflect the active atmosphere of the picture;

Open the city gate, middle arch bridge and tailgate; The three places are higher than other common scenes, but they are relatively high, medium and bottom, which makes people feel "the book is shocking, the middle volume is smooth, and the volume is closed".