Sylhet (Bengali: সিলেট) is a metropolitan city in northeastern Bangladesh. It is the administrative seat of the Sylhet Division. Located on the north bank of the Surma River at the eastern tip of Bengal, Sylhet has a subtropical climate and lush highland terrain. The city has a population of more than half a million and is one of the largest cities in Bangladesh after Dhaka, Chittagong and Khulna. Sylhet is one of Bangladesh's most important spiritual and cultural centres. Furthermore, it is one of the most economically important cities after Dhaka and Chittagong. The city produces the highest amount of tea and natural gas. In 1303, the Sultan of Lakhnauti Shamsuddin Firoz Shah conquered Sylhet by defeating Gour Govinda. Sylhet was a realm of the Bengal Sultanate. In the 16th-century, Sylhet was controlled by the Baro-Bhuyan zamindars and later became a sarkar (district) of the Mughal Empire. Sylhet emerged as the Mughals' most significant imperial outpost in the east, and its importance remained as such throughout the seventeenth century. British rule began in the 18th century under the administration of the East India Company. Sylhet became a key source of lascars in the British Empire with its ancient seafaring tradition. The Sylhet municipal board was established in 1867. Originally part of the Bengal Presidency and later Eastern Bengal and Assam; the town was part of Colonial Assam between 1874 and 1947 when following a referendum and the partition of British India, it became part of East Bengal. The Sylhet City Corporation was constituted in 2001. The Government of Bangladesh designated Sylhet a metropolitan area in 2009. The hinterland of the Sylhet valley is the largest oil and gas-producing region in Bangladesh. It is also the largest hub of tea production in Bangladesh. It is notable for its high-quality cane and agarwood. The city is served by the Osmani International Airport, which is named after General Bangabir M A G Osmani, the Commander-in-Chief of the Mukti Bahini during the Bangladesh Liberation War. People from Sylhet form a significant portion of the Bangladeshi diaspora, particularly in the United Kingdom and the United States and other countries in the Middle East.