For nearly four hundred years many maps of Asia, and particularly India and Southeast Asia, depicted an enormous lake far to the northeast of the Bay of Bengal. This lake, alternately called Chiamay, Chiam-may, Chian-nay, or Cayamay, is postulated to be the source of four to five of the great Southeast Asian river systems, the Irrawaddy, the Dharla, the Chao Phraya, the Bramaputra, and the Mekong. Today we know that the Lago de Chiamay is entirely non-existent, but where did this persistent myth come from?
The earliest reference to the Lago de Chiamay that we have been able to come across is the c. 1550 geographical study produced by Jao de Barros. Barros, who is not known to have traveled to the orient himself, compiled his geography from reports from Portugese explorers in the region, who themselves no doubt extracted many of their ideas about the remote interior of Asia from indigenous authorities. His most likely source for our purposes is most likely Fernao Mendez Pinto. Today the Barros geography is unfortunately lost, but some of its commentary survives via G. B. Ramusio and his 1554 edition of “Navigationi et viaggi”. While some have argued that Ramusio could not have possibly have had access to Barros’ commentary, as it had not been published at the time, Ramusio himself provides clear reference that he did in fact have an unpublished Barros manuscript. Ramusio includes several maps in his “Navigationi et viaggi” that were drawn around 1550 and depict the Lago.
Fernao Mendez Pinto, Barros most likely source and the lake’s supposed “discoverer”, is the only European who claims to have visited the lake itself. Pinto apparently discovered the lake in 1744. Generally speaking, while Barros was well respected in his day, Pinto is considered an unreliable geographer at best and at worse has been dubbed the “prince of fiction”. Why this is the case when he was without a doubt actually in Siam, may be explainable when his own sources are evaluated. Pinto may have heard about the lake in the Royal Court of Siam, one of the kings of which is said to have invaded Chiamay and captured many cities around it.
That Pinto derived much of his geography from local sources is highly likely. What he and his readers back in Europe may not have counted on is the presence of a mythical and semi-mythical Hindu-Buddhist geography overlaying the actual geography. Hindu and related Buddhist mythology consider Lake Manasarovar and Lake Rakshastal, in modern day Tibet, to be the spiritual source of four religiously and geographically important subcontinent rivers, the Brahmaputra, the Karnali, the Indus and the Sutlej. As the Hindu-Buddhist culture expanded into southeast Asia, these four rivers and their source lake were reassociated with local rivers such as the Irrawaddy, the Dharla, the Mekong, and the Chao Phraya.
From a European perspective, associating these rivers systems with one another and with a single source is an almost natural assumption. All five rivers bear a great deal of similarity. That is, all seem to originate from roughly the same area, all flow along roughly parallel courses, and all have enormous fluvial volume. Associating a great lake with said source is equally natural. Given the size and orientation of these river systems, one naturally speculates that the source lake itself must be enormous. Such speculation was not uncommon for map makers working in the 18th century and earlier. Cartographers, who rarely traveled the world themselves, had the difficult job of piecing together and interpreting various vague and often contradictory traveler’s accounts as well as reconciling such new information with accepted mappings.
Whatever the original source for the Lago de Chiamay may have been, it begins appearing on maps as early as the Gastaldi map of 1550 (though some speculate that this map was actually drawn a few years earlier). The Lago was embraced by Ortelius in his c. 1570 mappings of Asia and was eventually associated with various hopeful fantasies of a river passage through central Asia to the North Sea. Almost all subsequent mappings until the late 18th century included the Lago de Chiamay in various forms. Later, as explorers began to penetrate the region with greater regularity, Chiamatwas at various point associated with any lake discovered in the area, including Koko Nor (Qinghai Lake) in China and the actual Lake Manasarovar in Tibet. By the late 18th century the lake had moved far west of its original location and been reduced to a fraction of its original size. By the 19th century, it disappeared entirely.
The source of the name itself, “Chiamay” may be derived from Pinto’s original discovery of the lake in the records at the Royal court in Siam. Pinto was told of a royal raid to conquer and claim Chiang Mai, once the Capital of the Lanna Kingdom.
Sven Hedin discusses this lake and its origins in great detail in his fascinating and well researched 1919 article, “Early European Knowledge of Tibet”.
REF: Hedin, Sven, “Early European Knowledge of Tibet”, Geografiska Annaler, Vol. 1 (1919), pp. 290-339. Carpentier, Jarl, Some Additional Remarks on Vol. 1 of Dr. Sven Hedin’s ‘Southern Tibet’, Geografiska Annaler, Vol. 1 (1919), pp. 269-289