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and the rocky shores, however, were serious impediments for the development of inter- provincial and inter-insular traffic along the south coasts of Java and Bali. In accordance with the geophysical situa tion, Javanese cultural and political history had three centres consecutively: the basins of the southern rivers Opak and Praga, the basin of the Brantas and the eastern and central North Coast districts. The Begawan and its principal affluent, taking their rise in Central Java, provided means of communica tion between the central inland districts and the North East Coast. The Sërayu basin, however, did not become a centre of civiliza tion of any importance in the course of Javanese history. The three politically and culturally im portant centres of the Javanese land, for short henceforth called Central Java, East Java and the Pasisir (the Coast districts), made their appearance in history in conse quence of the activities of Indian traders and immigrants. The Indians’ motives for sailing to the southern islands are a matter of conjecture. Originally the finding of rich gold sediments in the rivers may have been the inducement. Afterwards the extraordi nary fertility of the soil and the regular supply of water for irrigation made settling among the Javanese indigenous tribes attrac tive. Probably the Javanese have known how to grow rice on terraced and irrigated fields since a very early period. Gradually the gold sediments in the rivers became exhausted, but in the meantime indigenous Javanese political organization had partly been In- dianized, and Indian religion, literature and art had acclimatized in Java. No doubt this acculturation of elements of Indian culture

in Java was made easy by the presence of a pre-Indian indigenous social organization of considerable refinement. The intricate sys tem of irrigation indispensable for an exten sive cultivation of rice on terraced fields (sawahs) presupposes a stable organization of labour directed by a powerful authority, either a single ruler or a dominating family oligarchy. Already in the pre-Indian period, in the first centuries of the Christian era, Javanese agricultural communities, though not numerous and scattered over a wide area in the jungle, may have known such author ities. For a very long time Javanese harbours on the North Coast had an important func tion in South East Asian trade as inter mediaries between the Continent and the Spice Islands, The abundant supply of rice available in Java was indispensible for trading vessels on their long voyages both east-bound and west-bound. For centuries Javanese rural communities living in the North Coast districts had the opportunity of acquainting themselves with continental culture by intercourse with traders and sailors who used to spend many months or even years in Java before continuing their voyage or returning home. In this manner the Muslim Faith was introduced into the island. Since the rise of Islam in Java in the fifteenth century, maritime commerce along the coasts of the Java sea was operative in spreading Javanese culture and enlarging the area where Javanese speech superseded autochthonous idioms. The East Javanese Muslim port of Grësik was the centre of proselytizing in far-off Lombok, where a flourishing Islamic literature written in a