Last updated August 24, 2018 at 4:46 pm
Modelling of sea level changes reveals original lagoon location.
For more than 1,000 years, across the Roman and Medieval periods, the city was a highly influential seaport, serviced by its port, known as the Portus Pisanus.
Evidence suggests the port was established around 200 BCE in a naturally protected lagoon that connected with the Ligurian Sea.
In the fifth century CE it was described as “a large, naturally sheltered embayment” that was used by maritime vessels. Between 1000 and 1250 CE, however, the surrounding coastline changed significantly, shifting more towards the sea and restricting access.
By 1500 CE the lagoon had all but disappeared, transforming into a coastal lake.
A new maritime port, Livorno, was built in the sixteenth century.
Since then, the exact location of the original Portus Pisanus has been a mystery.
“Despite its importance, the geographical location of the harbour complex remains controversial and its environmental evolution is unclear,” write a team headed by David Kaniewski from France’s Université Paul Sabatier-Toulouse in the journal Scientific Reports.
To try to resolve the confusion, Kaniewski and colleagues used a combination of biological and geological approaches to reconstruct relative sea levels over a period of 10,500 years and thus model the effects of sea level rise in shaping the harbour basin.
They also created an 8,000-year history of the environmental dynamics affecting the basin. Written accounts and archaeological artefacts arising from the Roman period were then compared to the findings, producing clearest indications yet of the lost harbour.
The results show how wetlands that developed around river outflows gradually developed into a navigable lagoon as sea levels rose, spurring the construction of the port.
The harbour facility became one of the most important assets for the Mediterranean world and remained so for many centuries. However, the modelling reveals that the same geographic process that formed it also doomed it. From the time the first ship docked, the clock was ticking.
“The site where the harbour complex was located was both its strength and its weakness because,” the researchers conclude.
“Like other deltaic contexts, sediment supply eventually entrained its demise. Portus Pisanus was destined to disappear due to long-term coastal dynamics and environmental change.”