The single arch of the Ponte Rotto (Broken Bridge) is all that remains of what was once the Pons Aemilius, the first bridge in Rome to be built completely out of stone.
For the purposes of defence, it was common for the piers of a bridge to be made of stone, but for the arches and the crossing to be made of wood. These could then be quickly dismantled, in the event of an attack.
The Pons Aemilius dates back to 179 BCE, but, over the course of the centuries, it was rebuilt several times. The flood of 1598 destroyed the eastern half of the bridge, which was then abandoned for two hundred and fifty years.
In 1853 Pope Pius IX had what was left of the bridge connected to the other bank via an iron footbridge. However, in 1887 most of the bridge was destroyed in order to make way for the Ponte Palatino. All that survives is a single arch.