Looking at a map of the Mediterranean Sea depth contours attentively, one is surprised at the incredibly complex nature of the sea floor: mountain ridges that cut across abyssal plains, isolated landforms rising from the seabed, real submarine mountains, valleys and deep canyons forming a rough and complex scenery, that is quite similar to the landscapes visible on the surface. There is a great curiosity to know what is hidden under the surface of the sea, to discover how the morphology of the coasts continues underwater and to know the processes that have led to the modelling of the submarine sceneries.