A THOUSAND QUESTIONS 
What happened then in the V century A.D. in Olbia? What caused the sinking of these great ships which were abandoned on the sea bottom, leaving the port unfit for use? What annihilated the city, preventing it from resuming trading?
The Answer
This event fits into the picture of the great Vandalic invasions which put the Mediterranean to fire and sword, destroying the immense power of the Roman Empire. Olbia, the main link in Rome's trade with Sardinia, was attacked and destroyed.
For centuries, the city's harbour lay silent. Olbia was no longer the great maritime city it had once been, and its harbour remained inactive due to the presence of the great Roman ships.
However, excavations indicate that in the XIII century, the city was once again thriving.
In that period, in fact, Olbia (then called Civita and capital of the Giudicato of Gallura) again started sea trading, as the result of an alliance with the Pisan Maritime Republic.
