The Pirenne thesis is superficially plausible. However, McCormick’s Origins of the European Economy, which represents perhaps the most innovative approach in dealing with a paucity of evidence to date, suggests otherwise.
“About one in seven eastern travelers I have uncovered set out from the Arab world (49: 14 percent of 340). They were mostly Christian and Hellenic. That so many appear from research geared to the Byzantine and Latin source materials—presumably the least rewarding for the Arab world—challenges the conventional wisdom.” [p. 217]
“Another, less obvious characteristic of some other eastern travelers further undermines the notion of interrupted intercourse, at least between Byzantium and the Arab world. Beyond the travelers who came directly from the Arab world to the west, another substantial group of eastern voyagers (28: 8 percent) also traveled to the Arab world at other times. In all, nearly a quarter of all eastern travelers also came from or went to the Caliphate (77: 23 percent of all eastern travelers).” [p. 218]
Moreover, though I shan’t here give references, a substantial portion of the European economy was driven by the supply of slaves to the Caliphate. But a few more things to note: the Arabs are just as important as the Byzantines insofar as the numismatic evidence is concerned; one writer during this period wrote of relief when arriving in the areas ruled by the Arabs, which were far more orderly—all that was needed was a simple bribe, a welcome prospect compared to the banditry common in other areas; Arab piracy was certainly widespread, but in McCormick’s analysis “very few of our travelers had their voyage interrupted by violence” [170] overall, whether by Arab pirates or other actors.