According to Strabon, a nearby river, Salsa (the current Capodifiume, near the southern wall and spanned by a bridge from the 4th century BC), created a marsh and changed Paestum into an unhealthy place .
It was the gradual siltation of the estuary, and the progression of the beach, which probably prevented the stream from flowing normally and stagnated.
Archeology reveals how the inhabitants tried to adapt by raising the level of houses, or by building pipes.
In fact, the Paestans moved north around the temple of Athena.
Its sanded port, away from the trade routes, life went out little by little.
The temple was transformed into a church. Note that in Paestum, there is an interesting example of religious syncretism, where the Madonna del Granato is related to one of the representations of the goddess Hera.

Although dived since the fifth century, Paestum was deserted by its inhabitants between the eighth and ninth century, especially because of malaria. The raids of the Saracen pirates forced the population to take refuge on the heights of the Mount Calpazio, where the city of Caput Aquae was established, identifiable with the current Capaccio. The cult of Santa Maria del Granato was brought there.
In the 11th century, the Norman Robert the Guiscard seized marble and sculptures of the ancient city to build the cathedral of Salerno.

Since then, the knowledge of Paestum was limited to a few scholars, until the mid-eighteenth century, when the fashion of the Grand Tour spread, born of the interest of many artists and scholars throughout Europe, including Paestum was an essential step.