Sauval says, “Lʹîle de la cité est faite comme un grand navire enfoncé dans la vase, et échoué au fil de lʹeau vers le milieu de la Seine.” This form of a ship struck the heraldic scribes, who, in the latter half of the Middle Ages, emblazoned it in the shield of the city. (SeeVengeur.)
When my ship comeshome. When my fortune is made. The allusion is to the argosies returning from foreign parts laden with rich freights.