Ricklefs (1991) identifies two overlapping processes by which the Islamisation of Indonesia occurred: (1) Indonesians came into contact with Islam and converted, and (2) foreign Muslim Asians (Indians, Chinese, Arabs, etc.) settled in Indonesia and mixed with local communities. Islam is thought to have been present in Southeast Asia from early in the Islamic era. From the time of the third caliph of Islam, 'Uthman' (644-656), Muslim emissaries and merchants were arriving in China who must have passed through Indonesia sea routes from the Islamic world.