established, except in exposed frontier zones, and certain cities developed a novel role as commercial centres. Even in areas where economic life remained depressed, urban values and traditions proved durable and helped to produce a social climate which later proved capable of responding dynamically to new opportunities.

Unity and Fragmentation in the Mediterranean World

'The whole sea shared a common destiny . . . with identical problems and general trends.' The historian Fernand Braudel's masterly study of the Mediterranean in the sixteenth century rests on an acceptance of its fundamental unity, which would be shared by students of the classical world. In the early Middle Ages the similarity of certain general trends cannot conceal the fact that the Mediterranean ceased to be a Roman lake, a channel of communication uniting a uniform area, and many historians have attributed the break with ancient culture and society to this development. The classic statement of this view was put forward in the 1920s and 1930s by the Belgian historian Henri Pirenne, who argued that the Arabs destroyed the unity of the Mediterranean in the seventh century and so paved the way for a distinctively western European civilization. Telling criticisms have been made of his approach and data, in particular his exaggeration of the extent of trade, his equation of economic activity with cultural achievement, and his pro-Roman bias. His provocative thesis also involves confusion of cause and effect; the Mediterranean did cease to form the cultural, political, and economic unit it had been earlier, but this fissure was in many respects a symptom of other developments.

Not only the consequences of this momentous change, but also its date and causes are difficult to establish. It has to be remembered that the Mediterranean is in fact a complex of seas, and that the degree of Roman naval control essential for regular trade and communication varied from one to another. In the easternmost basin, the Aegean Sea, Roman sea power and trade continued along traditional lines well into the seventh

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