‘Nothing that grows in the sea is perfect or noble. It is filled with caves and sand and endless mud.’ Socrates, to whom Plato attributes these words, would have been stunned if he had been able to travel forward in time to Venice, Lübeck, Constantinople or Alexandria in the late Middle Ages. In all these cities he would have seen intense maritime activity, bales of goods on the wharves, crowds of people around outbound ships, an aristocracy of businessmen grown rich by trade, mighty palaces overlooking the sea, as well as docks and warehouses, armouries and dealers, brokers and notaries. Where else did this fortune originate but from the exploitation of the sea? That is what this publication seeks to understand and illustrate, by untangling the strands of complex networks and exploring the interactions between space and time in a dialectic that could, in a Braudelian approach, be the basis for the research of all our collaborators. It leads us from the Mediterranean, mother of all civilisations, to pre- and post- Mongolian China, from the northern seas to America's pre-Colombian societies, and through the Middle Ages that, while it may not be considered important in all regions of the world, is nonetheless typically defined as the period from the 4th to the 15th century. While stopping short of obsessively seeking out superficial similarities between the regions studied, the hypothesis of the critical role of maritime activity in the rise of human communities deserves to be tested.

A successful investigation into the role of the sea in history and in the birth of modern capitalism would not have been possible without the cooperation of many experts. More than seventy medievalist historians responded to our invitation, from Western Europe and Russia, China, India, Japan, North America and the Caribbean. We asked each of them to reflect on the link between the exploitation of the sea and the prosperity of the cities, nations and States that turned to the high seas for essential resources such as salt and fish, but also for commercial and cultural interactions, and as a means both of transportation and supply.