Ancient civilizations lived in the fertile land along the Nan River and its tributaries, as is evidenced by Stone Age tools unearthed near Phitsanulok.

The main course of migration during the metal ages probably ran along the coast of Thailand, but migrants also travelled inland along the Chao Phraya to the Nan Basin and other areas, where it was relatively easier to establish settlements.

[5] Some of the Nan River Mon-Khmer retreated into the hills as the Thai expansion continued, while others generally adopted dialects of the Tai language and blended into the culture of the new settlers.

[5] predator animal species, as well as malaria, tropical temperatures and other hardships, kept the population from expanding far from the river, despite the region's extremely fertile soil.

[5] Even in spite of urbanization along the river banks, most of the Nan Basin (aside from the river-side settlements) consisted of virgin forests until around the turn of the 20th century.

[5] One of the early river-side urban areas of the Nan emerging during the era of the Khmer Empire was Song Khwae, which over the years developed into the modern city of Phitsanulok.

Phitsanulok is the only place in Thailand where houseboats are legal, as they have been an important aspect of regional culture since long before the drafting of modern municipal law.

People of Phitsanulok still gather on houseboats and raft houses along both sides of the Nan River in the city, and adhere to a traditional way of life.