The Crusades: The Authoritative History of the War for the Holy Land

by Thomas Asbridge

For both Islam and the West, perhaps the most striking transformation wrought by the crusades related to trade. Levantine Muslims already maintained some commercial contacts with Europe before the First Crusade through Italian seaborne merchants, but the volume and importance of this economic interaction were revolutionised in the course of the twelfth and thirteenth centuries, largely as a result of the Latin settlement of the eastern Mediterranean. The crusades and the presence of the crusader states reconfigured Mediterranean trade routes–perhaps most powerfully after Constantinople’s conquest in 1204–and played a critical role in solidifying the power of the Italian mercantile cities of Venice, Pisa and Genoa. Europe’s adoption of Arabic numerals can also be dated to around 1200 and likely resulted from trade with Islam, though this cannot definitively be connected to contact with the ‘crusader’ world.