Sumatra is the westernmost and second largest island of Indonesia and is a wide island fringed with smaller islands off its western and eastern coasts. The Bukit Barisan, a volcanic mountain range, traverses its length, reaching a height of nearly 13, 000 feet at Mt. Kerinci. Rising in the Barisan range are several large rivers, including the Hari, Indragiri, and Musi. In the north is the great salt lake of Toba. Because of the hot, moist climate and heavy rainfall, the vegetation is luxuriant, and much of the eastern half of the island is swampland. The interior is covered largely by impenetrable rain forests.
Sumatra comprises eight provinces of Indonesia. It is a sparsely settled island, with the principal centres of Medan and Palembang. Other important cities are Jambi, Padang, and Bandar Laumpung. The four largest ethnic groups are the Acehnese, Batak, Minangkabau, and coastal Malays. In the interior highlands are found the Gayo-Alas and the Rejang-Lebong groups. Islam is the predominant religion, though there are many Christians among the Batak and the Gayo-Alas. Chinese, Arabs, and Indians live on the coasts, and some 15 different languages are spoken on the island.
Sumatra had early contact with the Indian civilization and by the 7th cent. A.D. the powerful Hindu-Sumatran kingdom of Sri Vijaya flourished under the house of Sailendra. The kingdom extended its control over a large part of Indonesia and also over the Malay Peninsula. By the 14th century, Sumatran supremacy had waned, and the island fell under the Javanese kingdom of Majapahit. The Arabs, who may have arrived as early as the 10th cent., established the sultanate of Achin (now Aceh), which reached its height in the 17th century and controlled most of the island.
Sumatra has immense natural wealth. About 70% of the country’s income is produced there. The island has some of Indonesia’s richest oil fields, its finest coalfields, and deposits of gold and silver. Its offshore islands are known for their tin and bauxite. Most of the country’s rubber is grown in Sumatra; pepper, coffee, tea, sugarcane, and oil palms are also grown on plantations. The Deli region around Medan is famous for its tobacco. Rice, corn, and root crops are raised for local consumption. Timber cut includes camphor and ebony.