The sea has become the land, in that it is now the usual medium of transit: not barrier but corridor

The discovery of the sea roads necessitated a radical re-imagining of the history of Europe. Try it yourself, now. Invert the mental map you have of Britain, Ireland and western Europe. Turn it inside out. Blank out the land interiors of these countries - consider them featureless, as you might have previously considered the sea. Instead, populate the western and northern eaters with paths and tracks: a travel system that joins port to port, island to island, headland to headland,  river mouth to river mouth. The sea has become the land, in that it is now the usual medium of transit: not barrier but corridor.

R. MacFarlane, The Old Ways (2012), 92-3