Europe was Christian, the place where Christ was worshipped. Another religion grew up alongside Christianity: Islam. Christianity dominated Europe. Islam dominated a far larger region ranging from Morocco to Mindanao, from Central Asia to Zanzibar. The two religions were intimately bound not only by the shared Old Testament but also by trade, politics, war, and even alliances. At a time when tensions between the Muslim and Christian worlds are intense, it is important to see how, alongside the tension, the two religions collaborated with and shaped each other.