This was an experimental bridge built in 1808, by a French engineer called De Haviland.
The idea was to build a similar bridge across the river. For some reason the bridge across the river was not built in this style.
This bridge used to swing about 3 inches at the keystone when people walk over it. In 1936 this bridge collapsed. All you can see now of the ‘hanging bridge’ is the two towers on either side and the fallen section made of brick and mortar.