Bernard the Monk's Itinerarium is a ten-page guidebook for pilgrims traveling from Rome and Bari to Babylon and Jerusalem. It has not been studied as a source for Mediterranean history. Bernard shows how the late ninth-century Mediterranean economy was characterized by religious ideology. Islam and Christianity acted differently in establishing the "ethos" of an economy of exchange. While Muslim law and authority channeled the exchange, Christian apocalypticism wished for its end. Bernard's apocalypticism was in particular a response to the Muslim occupation of southern Italy. Such a response has been regarded as typical of the "age of ignorance" about Islam. But Bernard was surprisingly knowledgeable, and his account illustrates a largely unknown chapter in the history of the Christian encounter with Islam.