Muslims have been present in Europe almost as long as Islam has existed, most commonly as merchants traveling across the Mediterranean and the Black Sea, but also as captives in war and, less commonly, as slaves. Before modern times there were three main periods that left significant traces of a Muslim presence in Europe. In 711 CE a mainly Berber army crossed from North Africa into Spain at Gibraltar, quickly expanding northwards until they were stopped by Charles Martel (c. 688–741) at the Battle of Poitiers in 732. Muslim rule was thus established in most of Spain. Centered in Seville and Córdoba, its hold over the northern provinces was never firm, and it was from that direction that the Christian reconquista gradually pushed back Muslim rule beginning around the late tenth century. The kingdom of Granada held out for more than two centuries until...