While the history of marine painting is focused on the modern era and its landscape realism, little academic attention is paid to the study of earlier representations. Yet, at a time of global change, these experiences place us back in the long term. As we prepare to confront new mental landscape ruptures - the colour of the oceans, the overexploitation of shorelines and the verticality of offshore wind turbines – the study of what has shaped our now-threatened vision of the coastline deserves careful observation. Indeed, because our perception of the shoreline is made up of the certainty that there is a coastline, a sky in horizontal perspective, a specific articulation of sea and land, and the vertical momentum of lighthouses, we forget too quickly that this imaginary is historically dated. It was born of a new vision of the world, which emerged at a time of cultural and religious mutation: the end of the Middle Ages. Several major mental breaks separate the Middle Ages from our own modernity, both in the Symbolist approach – in stark contrast to the Positivist representation that followed – and in the media used, from medieval painted manuscripts to the panels and oils on canvas of later centuries. Christianity and its biblical references inspired vast quantities of maritime and aquatic references in the medieval world. It's worth recalling here that the ship is a major cultural artifact. As a result, medieval imagery is overwhelmingly maritime. Painting the sea was a natural thing for artists, even if it served above all a symbolist approach linked to a Christian apprehension of the waves inherited from Antiquity. There is, then, a significant corpus of maritime and medieval pictorial material, but its reception still challenges our understanding of the birth of seascapes that followed. While a closer look at the maritime imagery of French painted manuscripts reveals several recurring themes, it also reveals a remarkable break that occurred at the end of the Middle Ages. While Symbolist representations emphasized a vertical layout that allowed us to see the depths of the water, the arrival of perspective in the 15th century brought the oceans into focus. This led to the emergence of the first representations of the swell, whose highly innovative production techniques reflect a change in understanding of the place of the seas in medieval cosmography. This change obliged artists to re-articulate the sky and the sea in their compositions. We must therefore distinguish between classic hydrographic symbolism and the birth of maritime topography in medieval pictorial art, which precedes the famous works of the Flemish Primitives, while at the same time providing the mental foundation on which the first seascapes were built by a new way of thinking about the world. At the end of the Middle Ages, a new wind was blowing through maritime painting. Paradoxically, the surfacing of the sea now authorized the painting of the seabed, not because of a new scientific realist vision, but rather because of a shift in religious readings. Christian symbolism remained everywhere, however, as this type of painting had not changed its cosmographic objectives and semantics. The sequencing of Creation was still essential, even in seemingly secular subjects, but the idea of the existence of waters from above seems to us to have been singularly tested. Sea and land were still distinguished by a clear border, but the introduction of surfaces opened a new artistic option, so that the object that really emerged from this evolution seems to us to be the notion of the coastline. Initially hesitant, painters began to populate their lands bordered by the sea, until a space in between appeared. Jan van Eyck's Jonas, circa 1440, was one of the first to dare this new space. Here we find the classic miniature composition: an image in two registers separated by a diagonal that delimits sea and land, but Jan van Eyck adds a short sandy triangle between sea and land. The pictorial birth of the coastline? Although following classical canons, the painter was carried away by the treatment of the surface, the movement of the swell, the reflections of the water and the distant scenery. After the wave, it's the reflections and cameos that attract attention in this medieval maritime art. Blue is the dominant colour, as it replicates more easily in skies spread out in subtle gradations. Why, then, did he want to make the waves shimmer, if not to bring them into dialogue with the sky? Rather than a renewed Ocean, the artists have succeeded in re-articulating the sea with the air in the treatment of their perspective surfaces. Does humanity, still embedded between the two spaces, still perceive celestial space as a watery mass or as a firmament? Religious reform and humanism gradually dematerialized many medieval beliefs. The sea, now a mirror of the world, now answers to Heaven. While these painters pictorially invented the swell, the seabed and even the coastline, it was above all this re-articulated Heaven in the image of a rethought world that provided the foundation on which landscape painting and modern seascapes would later flourish. More than eight centuries now separate us from this great new aesthetic elaboration of the coastline. Eight centuries during which the redefined seascape has become part of our imagination. That's why, at a time when it's being deconstructed and we're talking about the acceptability of public policy in the face of change, we need to take the measure of its temporal power. It's also worth remembering that it is not independent of a taxonomy of the world that essentially stems from Western Christianity. Just as aggression against the ocean seems to us matricidal, the violence of change calls into question a worldview, prompting us to oppose such changes because we've unfortunately forgotten where they came from.