Cet article s’attache à poser les jalons pour une étude des aides à la navigation (phares et amers) et tente de les replacer dans le contexte des pratiques de navigation atlantique : navigation en droiture, navigation côtière, navigation dans les estuaires et dans les chenaux, navigation diurne et nocturne. L’érudition s’est généralement concentrée sur les phares – et, parmi eux, sur les plus spectaculaires –, qui n’ont pas toujours été les plus essentiels à la navigation et qui ont constitué une minorité des aides à la navigation. Un premier type de balise vise à se diriger depuis le large, nuit et jour, vers un port connu. La portée et l’angle de visibilité sont des données essentielles auxquelles on commence tout juste à s’intéresser. Ces balises peuvent avoir été de petites dimensions. D’autres localisent des dangers. Plus on s’approche de la côte, plus les amers identifiables, disposés en système, permettent au pilote de se situer et de tracer sa route dans un espace théorique issu d’une construction cognitive du paysage. Les traces laissées par ces amers, dont seul un petit nombre a été conçu spécifiquement pour être une aide à la navigation, sont souvent très discrètes et seules des enquêtes de terrain spécifiques, à échelle réduite, sont susceptibles de révéler les systèmes d’aides à la navigation qui étaient plus le fait de la science du pilote que de l’intention d’un aménageur.
Navigation without a chart or instruments depended on a pilot’s knowledge and ability to use the wind, the stars and the reading of the landscape to safely steer a ship to its destination. There has been a growing interest in navigation aids over the last ten years. Ongoing studies, only a few results of which have been published to date, reveal that these navigation aids are extremely numerous in the Mediterranean area, but also that the archaeological traces they have left are often very subtle. Reconstructing the visual landscape of ancient navigators means abandoning the vision we have of it from the land and entering into the cognitive process of landscape design by the pilots. The methods of intellectual construction and the functions of daymarks vary according to the routes and the practices, the ships and the users. Navigation in a straight line, with a succession of days and nights at sea, was a common process within an area bounded to the north by Jutland and the British Isles, including Ireland, by Madeira to the west and by the Canary Islands to the south. Lighthouses, with a reach of 20 to 30 nautical miles, were built within these geographical limits. Their visibility depends on the height of the focal point. The height of the construction is practically only justified on a low shoreline, to compensate for the lack of altitude of the substratum. In A Coruña (Spain), a 40-metre-high tower made it possible to gain only 2.5 nautical miles of visibility compared to a 20-metre-high tower. The construction of higher and more complex monuments has to take other factors into account. Their “remarkable construction” reflects the importance of the sponsor. Generally speaking, the most monumental lighthouses are the best known. They have been observed for a longer time, are sometimes still preserved, and have been described in texts as being endless repetitions of the lighthouse of Alexandria (Egypt). They can give rise to a biased view of reality. The example of the Mediterranean highlights the extreme diversity of these structures that are visible from a great distance, sometimes identified by their inscription. Alongside stepped constructions with a square plan, inspired by the Alexandrian lighthouse, which characterise the tallest towers, there are circular towers topped by a furnace and intended to guide ships safely into port. There are characterized by extremely small dimensions (5 m in diameter). On higher shorelines lighthouses were probably more numerous, but they left very poor traces that are difficult to identify using archaeological methods. Nocturnal coast markers directed towards the open sea were not only constructed at an early date, they were also numerous. They were hierarchised on the basis of the height of the focal point, which made it possible to distinguish the directional light from a greater distance, and to spot it at a greater height compared to other lights defining a landscape, a coastline, its important positions and dangers. Closer to the coast, where navigation was more often practised in the daytime, location within the space involves a complex cognitive process that combines knowledge about the seabed (depth and nature) and a landscape reduced to the horizon line. In this case the relative arrangement of the daymarks allows a pilot’s expert eye to determine where they are and to choose the route to their destination. Each user establishes their own points of reference on the cognitive map of their maritime space. Only a tiny minority of these were designed to be daymarks, except on low shorelines, where they are a necessity. Maritime sanctuaries and funerary monuments intended to be visible occupy an important place among the daymarks. On the other hand, daymarks –because of their nature, not their purpose–, are necessary to mark channels, for example port entrances or estuary channels. A variety of solutions existed: stone-built benchmarks at harbour entrances, aligned daymarks to indicate the navigation channel, marking of the channel with piles or floats. Towers could signal low currents. As is the case in other regions, the study of the Atlantic maritime cultural landscape takes us to the heart of the diversity of its markers, its users and their ships. It involves the reconstruction of the often very subtle, but no less essential, elements of a landscape that takes on its meaning only when seen from the sea, through a cognitive construction that is proper to category of user of the maritime space.
