78 dominique valérian
world economy in formation, a centrality that increased during the late Middle Ages,
only to be partly lost after the discovery of America and the European circumnaviga-
tion of Africa.
As a central space where no power could completely triumph despite the hegem-
onic aspirations of the most powerful states, the medieval Mediterranean was thus a
border—a place both for exchanges, which became more intense over time, and for
political, ideological, and economic competition. Historiography oscillates between
two poles: the image of a world criss-crossed by merchant ships, regulated by peace
treaties and by the values of the mercantile world—an image that combines nostalgic
memories of the unity and peace of Roman times with the ideal of an Andalusian
convivencia between Christians, Jews and Muslims (compare Catlos, this volume);
and the dark image of a sea of wars, dominated by the centuries-old confrontation
between cross and crescent—crusade, jihad, and piracy, their corollary at sea (Backman,
this volume)—but also by the competition between great powers with hegemonic
aspirations. But if some periods were marked by an intensification of conflicts, more
often exchanges and conflict coexisted, and the increase of maritime trade encouraged
both competition for control of strategic ports and shipping routes and the search for
diplomatic agreements promoting trade.
Changes of equilibrium in the medieval Mediterranean were the result of political
and military competition (sometimes limited to a portion of the sea, sometimes larger)
but also of transformations in trade networks. In either case, the situation in the
Mediterranean cannot be isolated from broader changes, sometimes with roots in
very remote areas. In the seventh century, the emergence of Islam opened a conflict
between two universal monotheistic religions, mainly with Byzantium at first, then
with the Latin powers of western Europe. It would be wrong, however, to reduce the
wars in the Mediterranean to this religious conflict: wars between Muslim powers
(Fatimid against Umayyad, for example) or Christian ones (Genoa against Pisa,
Venice, or the Crown of Aragon) were much more numerous and persistent. But
beyond that permanent competition—the military competition for political dominion
and the commercial competition for control of the exchange networks—the Middle
Ages were above all a moment of the construction of modalities of interactions in a
shared space, of the control and regulation of both exchanges and conflicts. This
construction proceeded through the numerous diplomatic negotiations of the period
(aided by the work of jurists) and, above all, by the increase in shared practices that
eventually became general customs in the Mediterranean. This progressive construc-
tion of rules for this “in-between” space permitted the re-creation of the unity lost
after the fall of the Roman Empire. This is the legacy of the Middle Ages to the
modern era.
The “breakdown of Mediterranean unity”Published posthumously in 1936, Henri Pirenne’s Mohammed and Charlemagne
sparked a major debate, far from resolved today. According to the Belgian historian,
the unity of the classical Mediterranean, maintained beyond the Barbarian invasions,
was permanently ruptured by the Arab conquest: “The sea which had hitherto been
the center of Christianity became its frontier. The Mediterranean unity was shattered”
(Pirenne, 1957: 152–153). The end of political unity, then, caused a slowdown of