The zone between Burma and Siam, established by an agreement between Great Britain and France dated the 15th of January 1896, declared " the portion of Siam which is comprised within the drainage basin of the Menam, and of the coast streams of a corresponding longitude," neutral as between them.
(For map, see Indo-China.) The country may be best considered geographically in four parts: the northern, including the drainage area of the four rivers which unite near Pak-Nam Po to form the Menam Chao Phaya; the eastern, including the drainage area of the Nam Mun river and its tributaries; the central, including the drainage area of the Meklong, the Menam Chao Phaya and the Bang Pakong rivers; and the southern, including that part of the country which is situated in the Malay Peninsula.
Between these ranges flow the rivers Meping, Mewang, Meyom and Menam, turbulent shallow streams in their upper reaches, but slow-moving and deep where they near the points of junction.
The Meping and Mewang on the W., rising among the loftiest ranges, are rapid and navigable only for small boats, while the Meyom and Menam, the eastern pair, afford passage for large boats at all seasons and for deep draught river-steamers during the flood-time.
The Menam is the largest, deepest and most sluggish of the four, and in many ways resembles its continuation, the Menam ChaoPhaya lower down.