At the same time as the fleets of Pisa, Genoa, Venice, and other maritime powers of the Christian West were confronting the navies of the Fatimids and Ayyubids in the waters of the Levant, a far wider confrontation at sea was beginning all over the Mediterranean; a confrontation whose outcome was to have infinitely greater importance in the long term than the wars of the Crusades. In the eleventh century there commenced a decisive movement by the merchant marine of the Christian West to establish its dominance over those of Byzantium and Islam in Mediterranean maritime shipping and commerce. In fact, of course, and particularly because of the key role played by the guerre de course in both, the essentially naval and strategic struggle between the three civilizations on the one hand and the competition in maritime traffic on the other were integrally connected and part and parcel of the same historical phenomenon.

Because of its complex and multiplex nature, the parameters and evolution of this competition in maritime traffic between the merchant marines of the three civilizations are even now obscure, despite an enormous historical scholarship devoted to the subject over the past century. The rich European archives have been ransacked to document what was beyond a shadow of doubt an enormous growth of shipping and maritime commerce in Western seaports such as Genoa, Pisa, Venice, Marseilles, Barcelona, Montpellier, and Dubrovnik.