[9] The earliest historical record mentioning the Haru kingdom was a Chinese chronicle dated from the Yuan dynasty (late 13th century).

[2] The Benteng Putri Hijau archaeological site, at an ancient fortress near Medan, shows several layers of cultures estimated to date from between the 12th and 18th centuries.

The fort is in the Karo and wider Batak tribes' tradition of constructing huta or kuta, a walled compound completed with parik (moat) as a defensive structure to protect the village against incessant tribal warfare.

[7] A fragment of lingam was discovered at the nearby site of Sukanalu, suggesting that the population of Aru adhered to both native animism and Hinduism prior to Islam entering the region.

According to Pararaton, Haru kingdom was mentioned among polities that Gajah Mada intended to unite under Majapahit suzerainty in his Palapa oath.

According to Yingya Shenglan (1416), a Chinese Ming dynasty report composed by Ma Huan about the Zheng He expedition, the king of Haru and his subjects had embraced Islam.

The discovery of Muslim headstones at burial sites in Kota Rentang suggests that the ruling elites of Aru Kingdom, the King and his family, has converted to Islam.

These Islamic headstones are made from volcanic tuff with Arabic Jawi script similar to those found in Aceh and other Malay states.

Numerous artifacts have been discovered at this site, including Islamic headstones, ceramics and pottery fragments from China, Thailand and Sri Lanka, and Arabic coins from the 13th and 14th century.

[2] Both the Malaccan Malay and Portuguese sources mention the demographic split, and sometimes rivalry, between the Muslim minority of the coast and the native pagan heathen majority of the island, with their notorious practice of cannibalism.

"[14] The Portuguese record Suma Oriental, written in the early 16th century mentions Aru as a prosperous kingdom with plenty of rice, meat, fish and wine.

Two decades later, Mendes Pinto also recorded the presence of the people of "Aaru" on the northeast coast of Sumatra where he also visited the local Muslim king.

[15] Aru steadily grew weaker in the 16th century, caught in a regional rivalry between more powerful neighbours — Portuguese Malacca and the Sultanate of Aceh.

Because of the incessant pressure from Aceh in the early 16th century the capital of Aru moved inland, from coastal Kota Rentang to Benteng Putri Hijau.

In 1613, the ambitious and warlike Sultan Iskandar Muda of Aceh, strike a final blow to seal the fate of Aru kingdom.

[9] Archaeological excavation has uncovered fragments of lingam, which suggests that part of Aru's society, possibly Tamil settlers, adhered to Hinduism.

[12] The Chinese sources mention that the culture of Aru, areas such as customs, marriage and funeral traditions, language and trade, are quite similar to those of Malacca, Pasai and Java.