According to their ethnographers, the Bena of the Rivers in colonial Tanganyika emerged ‘from the shadows into the light of day’ when they undertook a great migration from the forested hills of the Iringa highlands to the treeless floodplain of the Kilombero valley in the late 1800's. The phrase had two meanings – on one level, it described the physical relocation of the Bena from the shadows of the forest to the open floodplain. On another level, ‘light of day’ was a metaphor for the remembered cohesion of a distinct Bena tribal identity, distinguishable from the ‘shadows’ of prior ethnic obscurity. The Culwicks considered the chief or mtema of this period, Ndaliwali, to be the founding ancestor of a new political lineage.

The defining moment for the emergence of the Bena of the Rivers was the Battle of Mgodamtitu in 1874, when neighboring Hehe attacked Bena settlements in the foothills and forced the Bena permanently out of the highlands and into the valley. Once they had taken up their new residence, the Bena absorbed the existing settlements of the western end of the valley into their kingdom. They did this initially ‘under the guise of protector’, wrote the Culwicks, but their goal was political control of the region. By 1890, they wrote, most of the Ndamba as well as several smaller valley groups had become subjects of the Bena chief.

The Battle of Mgodamtitu caused a ‘sudden and wholesale change’, according to the Culwicks, because Bena were forced to give up cattle keeping and take up rice cultivation; to learn the ways of the river and skillful use of canoes. They had previously looked down upon ‘rice and fish-eaters’, but after their migration they found that ‘there is but one crop really worth growing, and that is rice’.