The terrain of Burma is very mountainous but not uniformly so. There are parts of the area where the valleys between the mountain ridges are narrow gorges where no human habitation is possible except for those who are prepared to scarp a livelihood from the steep mountain face. But elsewhere the valleys form flat well-watered alluvial basins perfectly adapted to the needs of the rice farmer. My terms "Hill People" and "Valley People" are intended to denote the diametrically opposed modes of subsistence associated with these two types of terrain. These two modes of subsistence have been present in the area throughout historical times2 and any hypothesis concerning historical process must take this into account