The Chao Phraya River basin covers most of modern central and northern Thailand and is bordered to the west by rugged Burmese mountains, to the north by lofty mountains separating southern China from the Southeast Asian mainland, and to the east by the high, sprawling plateau settled by the Ban Chiang people. Easily accessible only from the southern Gulf-of-Thailand coast and the southeast (present-day Kampuchea), the Chao Phraya river basin was well protected from excessive outside influence and sudden, massive incursions of new settlers.

A natural, self-contained geopolitical unit, this river basin was destined to play a central role in Thailand's development, becoming historically and agriculturally as important to the Thais as the Nile is to the Egyptians. Later, it would become the Thai hertland and contain future Thai capitals and for centuries remain the major means of transport and communications. Eventually, it would be transformed into and intricately terraced, irrigated rice bowl figuring among the most fertile areas on earth.

The influx of immigrants into the area took hundreds of year. They came in successive waves, each moving slowly along paradisical river valleys content to settle rather than move on. Those following moved past them to hew out homes and fields from virgin forest. Traveling in compact groups, under separate chieftains, escaping famine, despotism or misfortune, all sought a degree of autonomy and shared a comman desire for a better, independent life.