From the late first millennium AD, vast Indian Ocean trade networks extended as far south into Mozambique as evidenced by the ancient port town of Chibuene. Beginning in the 9th century, a growing involvement in Indian Ocean trade led to the development of numerous port towns along the entire East African coast, including modern day Mozambique. Largely autonomous, these towns broadly participated in the incipient Swahili culture. Islam was often adopted by urban elites, facilitating trade. In Mozambique, Sofala, Angoche, and Mozambique Island were regional powers by the 15th century.