The correct answer is - Marseille.
The port in question is Marseille. Since the forming of the settlement by Greek colonists its purpose has been to serve as strategically well positioned port, and this has remained the same as the centuries passed by, just that the importance of the Marseille port grew bigger and bigger over time. Nowadays it is by far the most important French port, one of the most important in Europe, and one of the most important in the world as well.