The Pons Cestius goes across to Trastevere, today considered to be the epitome of a Roman popular quarter. We do not know exactly when this bridge was built but it dates back to the same period as the Pons Fabricius, which is in much better condition.

Most of the original had to be pulled down during the shoring up of the river bank. In ancient times, the river was not just a natural boundary to the city but it had a religious significance as well. The gods had intended the river to keep the two banks separated and so, any human attempt to link them was a kind of contravention of divine law.
The construction of a bridge was a sacrilege. Only the High Priests, the "Pontifices", had the right to celebrate the rituals and to decide when a bridge could be built. The word "Pontifex" literally means "bridge builder".
For a long time, the Tiber's right bank was the area where foreigners had their residences because non-citizens did not enjoy the right to live in the Pomerium, the sacred city limits.