Indian Ocean

The wind over this ocean blows from the southwest for half the year and the northeast for the other half, which means a ship can sail out and be certain of a way home. Michael Pearson's history argues that this single physical fact organised everything else: a merchant sailing from Gujarat to the Swahili coast had to wait months for the wind to turn, and so lived, married, prayed and built in the port he had reached. Religion travelled as a consequence of waiting, not of conquest.

The first great transfer went east. Indian traders, and the brahmins and monks who accompanied or followed them, carried Hindu and Buddhist ideas of kingship, cosmology and temple form to the coasts and river mouths of Southeast Asia in the first millennium, and the results stand at Borobudur and in the Khmer temple mountains. The transmission was not an empire; it was a long conversation carried on the same winds as the pepper.

Islam followed the same routes and used them more thoroughly. By the thirteenth century Muslim merchant communities were established from Mogadishu to Malacca, and conversion in coastal Southeast Asia proceeded largely through trade and marriage rather than through armies. Engseng Ho's study of the Hadrami sayyids, families claiming descent from the Prophet who spread from the Hadramawt valley in Yemen across the ocean, follows a diaspora held together by genealogy, marriage and the tombs of ancestors, and shows how a religious lineage could function as an ocean-wide institution.

The Saint Thomas Christians of Kerala hold that the apostle Thomas landed on the Malabar coast in 52 and founded churches there before dying at Mylapore. The tradition is old and the community is unquestionably ancient, with documented links to the Church of the East in Persia from at least the fourth century; the apostolic voyage itself rests on tradition and the apocryphal Acts of Thomas rather than on contemporary record, and historians differ on it. Either way, the community is evidence that Christianity reached India by sea long before it reached most of Europe by land.

Pilgrimage was the ocean's other great traffic. Hajjis from Southeast Asia, India and East Africa sailed to Jeddah on the same monsoon schedule as the cargo, often spending a year or more away, and the pilgrim ships of the nineteenth century carried tens of thousands a season. The scholarly networks that resulted, students from Java and Sumatra studying in Mecca and returning as teachers, reshaped Islam in Southeast Asia repeatedly.

The coasts are lined with the results. Sufi shrines and saints' tombs stand at ports around the whole rim, from the Swahili towns to Gujarat to Aceh, serving pilgrims and, in many places, sailors making vows before a voyage. The ocean also carried a slave trade, from East Africa to Arabia, Persia and India, that ran for over a millennium and left communities of African descent around its northern shores.