Stone arched bridges, built up with stones into arched and curl shapes for the free flow of the water, can be found in both the south and the north and account for the majority of all bridges. The river courses in south China are narrow and deep and are heavily used by ships; meanwhile on the bridge, goods are mainly carried on the shoulders, so there is no need for the arch span to be too big, although the extrado is exceptionally high. The situation in the north is just the opposite. River courses are wide and shallow, and are not necessarily used heavily by shipping; transportation over the bridge is mainly by horse-driven vehicle. Therefore, the extrado need not, or cannot be, too high and the bridg6.surface is flat and gentle. This explains the difference in the styles ofarch bridges between the south and the north, with the former being curved, flexible, void and brilliant and the latter straight, solid and steady.

The oldest extant bridge of China is a single span stone arched bridge.- Anji Bridge in Zhaoxian County of Hebei Province, built in the Sui Dynasty (Fig.7-1)

Anji Bridge can represent the style of stone arched bridges of north China. Its builders boldly created a big span, bow-shaped arched, curl bridge. The arch span reaches 37.47 meters, the rise being less than one-fifth of this; the maximum height is 3.51 meters. The river under the bridge is often in flood after heavy rain. In order to help increase the sluice area during flooding between the large arch and the surface of the bridge, two holes are opened in each of the two shoulders arches. This method plays the role of lightening the overall weight, reducing 7engineering work and enriching the mold.

This is a Chinese pioneering development. The bridge Surface is in a gentle, convex round arc shape. In the bridge head, the arc line reverse is a slightly concave curve- The curve of the whole bridge is very beautiful and relaxed. The arc radius of the bridge Surface is fairly large, while the radius of the bridge rolling is small. One is relaxed and one is stretched. The relaxed one is on the upper side and the stretched on the lower side, forming an effective foil and contrast relationship. The small arch of the four open shoulders and the elevation of the extrado of the large arch move downward gradually from the center to the outside. Their orbit ligature is the arc line of the bridge Surface. The contrast between large and small arches demonstrates the real measurement of the large arch; the methods of various arches are identical and stress is placed on unity The permeability of the small arches makes the bridge appear to be empty, bright and light.

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