The birthplace of Homo sapiens, Africa throughout history has been home to numerous civilizations whose diversity belies the inclination to think of the continent as culturally undeveloped or uniform. Bordering on the Mediterranean to the north, North Africa saw the growth of a variety of cultures, first under the influence of Christian Byzantium and then under Islamic influence after the seventh century. North African port towns brought together people and goods from Europe, Asia, and Africa, making them cosmopolitan hubs centuries before the rise of European nation-states. Arab merchants traveled south from North Africa across the Sahara, carrying such wares as salt and ivory as well as the religion of Islam to Senegal and northern Nigeria. From the twelfth century on, Islamic theology and instruction made the town of Timbuktu on the Niger River an important cultural node in the trans-Saharan trade.