【地球科学】イタリアのピサにあった港の複雑な歴史

New insights into the evolution and eventual disappearance of Portus Pisanus, the lost harbour of Pisa, are reported in Scientific Reports this week.

Although it has been described as one of Italy’s most influential seaports during the Roman and Middle Ages, little is known about the relationship between Portus Pisanus’s environment and the main stages of its history.

To understand the role that long-term coastal dynamics, sea-level rise and a changing environment played in the harbour’s evolution, David Kaniewski and colleagues reconstructed relative sea levels for the eastern Ligurian Sea over a 10,500-year period. They also coupled historical maps with geological data to reconstruct the morphology of the coast around the Pisa harbour basin. They analysed biological samples from sediment layers to investigate how seawater, freshwater or agricultural activities may have influenced the environment in the area, before comparing and contrasting their data with written sources and archaeological data.

The findings suggest that at approximately 200 BC, a naturally protected lagoon with a good connection to the sea developed south of the city of Pisa that would have benefited navigation and trade, and facilitated the establishment of port complexes. The lagoon hosted Portus Pisanus well beyond the 5th century AD but its degree of sea connection began to decline from around 1000-1250 AD, as coastlines shifted towards the sea. It was cut off from the sea and disappeared around 1500 AD when the basin developed into a coastal lake and Portus Pisanus was replaced by the maritime harbour of Livorno.