Before the rise of the historic tribes, their indigenous ancestors lived along the river for thousands of years. In the Lower Mississippi Valley, they began building monumental earthwork mounds in the Middle Archaic period (6000–2000 BC in Louisiana). The earliest construction was Watson Brake, an 11-mound complex built about 3500 BC by hunter gatherers in present-day Louisiana. The discovery and dating of several such early sites in northern Louisiana has changed the traditional model, which associated mound building with sedentary, agricultural societies, but these cultures did not develop for thousands of years.