Subsequently, the independent Bengal Sultanate was established by the rebel governors in 1352. During their rule Bengal was transformed into a cosmopolitan Islamic superpower and became a major trading nation in the world, often referred by the Europeans as the richest country to trade with. The sultanate's ruling houses included the Ilyas Shahi, Ganesha, Hussain Shahi, Suri and Karrani dynasties, and the era saw the introduction of a distinct mosque architecture and the tangka currency. The Arakan region was brought under Bengali hegemony. The Bengal Sultanate was visited by explorers Ibn Battuta, Admiral Zheng He, and Niccolo De Conti. During the late 16th century, the Baro-Bhuyan (a confederation of Muslim and Hindu aristocrats) ruled eastern Bengal; its leader was the Mansad-e-Ala, a title held by Isa Khan and his son Musa Khan. The Khan dynasty is considered local heroes for resisting North Indian invasions with their river navies.