This bridge over the river Wye at Ross-on-Wye is built of red sandstone. It was built from 1597 to 1599, and was widened during the 1950s, by the addition of a concrete platform on the upstream side. It has a very unusual feature. Instead of the voussoirs having the normal slightly tapered trapezium shape, every one of them has a zig-zag shape on both sides. One of them has been outlined in white to show this more clearly, as the photograph is poor, because of the flat lighting.
An enlargement is inset at the lower left of the picture. It is as if the designer thought that there could be shear between each voussoir and its neighbours. This should not, of course, happen in a well designed arch.
Here is another picture taken with more favourable lighting, showing the erosion of the old red sandstone. Lighting can be very important if you want to reveal features of a structure. A similar type of joggled voussoir is seen in the facade of the Mosque of Ilyas Beg in Balat, Turkey, dating from 1404. There is also an arch with serpentine boundaries between the voussoirs.
Here is a picture of one arch. Note the flood relief arches in the distance, under the Ross-on-Wye bypass A40. The river Wye and the river Severn are very prone to flooding, which has caused great damage in several recent years.
Perhaps the designer had experienced a problem with a previous construction, and was trying to make sure that nothing could go wrong. If these shapes are to achieve anything, the stone must experience both shear and tension. What structures can exist which experience no shear and no tension? This bridge has very large cutwaters, perhaps because the Wye in spate has a very fast flow. A refuge for pedestrians is provided over each cutwater.
Here are two more pictures of the Wilton bridge at Ross-on-Wye. The piers are very wide, and the bridge presents a significant obstacle to the flow. History of Wilton bridge.