In 13th to 16th century, the Karo people believed has established Aru Kingdom (also spelled Haru), located in modern day Medan city and Deli Serdang Regency. It was one of the earliest kingdom in Sumatra. The population of Aru Kingdom adhered native animism, Hinduism and Islam. Islam slowly gained influence in coastal area since late 13th century. Despite among the earliest Sumatran kingdom that was exposed to Islam, the people of Aru kingdom remained predominantly pagan, especially those who inhabit interior region. The successor state of Aru Kingdom was the Sultanate of Deli, which demonstrate a mixed influences of Karo, Malay, Tamil and Aceh.