From late medieval times, a number of great emporia in the Indian Ocean provided structure and vitality to its seaborne trade. The overland caravan routes linking together China, Central Asia, the Middle East, India, and North Africa also passed through urban centres performing similar functions. To see the full social and economic dimensions of emporia trading, which called for the transport of goods and the passage of men over long distances, it is necessary to form a mental image of the historical contours that divided one Asian civilisation from another in our chosen period. Arab geographers, travellers, and historians, from the tenth century to the sixteenth, were aware at all times that they lived between two if not three worlds. The land of Islam, as al-Muqaddasi observed, was touched on one side by the Sea of China and on the other by the Sea of Rome. Africa was closer to the Arabs and the Persians than were India and China, and yet the continent had recognisable frontiers beyond which Muslims found themselves in an unknown and alien environment. The configuration, then, was not merely one of physical geography but also one of cultural identity. The traditional seafaring communities of the Indian Ocean, whether or not they explicitly adopted the religious teaching and the authority of the Quran, certainly welcomed and tolerated the presence of Muslim merchants, sailors, and migrants.