Lake Chimay
Lake Chimay or Chiamay, also known by numerous other names, was a fictitious lake or marsh which appeared in European maps of Asia throughout the Age of Discovery. Originating from accounts of Portuguese exploration of Indochina, it was believed to be an enormous lake about  inland from which several of the major rivers of Bangladesh, Burma, and Thailand flowed. It continued to appear in European maps, gazetteers, and encyclopedias into the late 18th century. Names
The name has appeared as Chimay, Cunebetét, Chiamay, Chiammay, Jangamá, Jangoma, Cayamay, Chiama, Jamahey, Chiamai, Chaamay, Chiama, Cunebete, and Singapamor. Given its use in João de Barros and Feenão Mendes Pinto both in reference to the lake or marsh and to the surrounding kingdom and its nearby capital, it appears to have originally taken its name from Chiang Mai, capital of the Kingdom of Lanna. History
In his Décadas da Ásia, João de Barros mentions the  in his treatment of the term of Lopo Soares de Albergaria, who was governor of Portuguese India in the period 15151518. Barros had previously met with Fernão Mendes Pinto, whose journal of his travels in the 1540s was later published, including two passages about a lake either 36 or 180 leagues around surrounded by prosperous mines and possibly originating the Ganges in addition to the other great rivers of the region. As , the lake was greatly popularized by the "Ramusio Map", a map of Southeast Asia drafted by Giacomo Gastaldi and used as the third map () in the 1554 second volume of Giovanni Battista Ramusio's . Gastaldi gave the lake as the origin of the Brahmaputra, Irrawaddy, Salween, and Chao Phraya. No major lake has ever existed in the area of Chiang Mai, butestablished by Barros and Ramusio's reputationsthe lake spread across new European maps as late as 1751 and continued in the form of reprints even longer, at least as late as 1783. During the same period, it continued to be mentioned in gazetteers and encyclopedias, including an entry in the first edition of the Encyclopaedia Britannica. See also
 History and Geography of Thailand
 History and Geography of Burma
 Age of Discovery
 History of cartography and geography
 Cartography of Asia

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 . . . . . Fictional lakes
Cartographic errors