The arches are elliptical in shape and they also vary in length with the longest span in the center. Pont Royal was one of the first bridges to use open caissons in its construction. Francosi Romain, a foundation expert from Holland, dredged the river bed to provide a firm level surface and then sank tall caissons that were pumped out to provide a dry place to build the piers.
Pont Royal is 110 m (360 ft) long with spans of 20.6 m (68 ft), 22.7 m (75 ft), 23.5 m (77 ft), 22.4 m (74 ft), 20.6 m (68 ft), and a width of 17 m (56 ft).
The cutwaters at the ends of the piers have conical tiled roofs, the balustrades are unadorned stone barriers, and the bridge was equipped with a gauge to show the previous high flow at this point in the river. It was thought (especially in the past) that the many bridges in the Seine tended to slow the river's flow and contribute to its flooding. More recently, there has been an effort to align the openings of the bridges to allow the river to flow downstream unimpeded.
Almost all the river bridges in Paris are arches. In the past, suspension bridges have been built over the Seine, but their towers and cables are an impediment to views of the city and they were eventually replaced with arch bridges. Paris is fortunate to have a river that is narrow, slow-moving, and shallow. The Huangpu River in Shanghai is over 500 meters wide and people still take ferries or drive across huge bridges to cross it (see January 26th's blog). The Hudson and East Rivers in New York City are also wide and require big bridges that dwarf people and their activities.
The Thames is similar in size to the Seine and affords many pleasant strolls over bridges. Tokyo has three moderately-sized rivers as well as many pleasant arch bridges.
Seine River Bridges: Pont Royal by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.