AT THE CROSSROADS OF CIVILIZATION 1. The Arab Conquests: Opening or Closure [19] The global impact of the Islamic conquests has been an issue of historical debate since Henri Pirenne formulated the problem a half century ago. In Pirenne's view, the conquest of the eastern and southern shores of the Mediterranean, of Spain, and of strategic islands had shut off the mainsprings of the movement of world trade which had flourished during the late Roman times, with the result that western Europe felt an intensification of ruralization and was impelled to return to a closed, moneyless, "natural" economic system. The conquests, then, set in motion a chain of events that was, centuries later, to result in the shifting of the balance of power in Europe from the Mediterranean region northward. In fact, the Islamic conquest had more nearly the opposite effect than that posited by Pirenne: it opened the Mediterranean, previously a Roman lake, and, by connecting it with the Indian Oc...