Around 1100, the proto-Chagga were probably settled on the southeastern slopes of Mount Kilimanjaro, although North Pare is also proposed as a possible primary settlement area. They already possessed a fully developed highland agricultural system in which bananas held extraordinary importance. This productive system gave the society a substantial advantage in a mountainous environment constrained by surrounding pastoral and Cushitic populations.

The source presents Chagga expansion as a major process of the following five centuries. The productivity of highland agriculture enabled Chagga communities to spread across Kilimanjaro while absorbing both East Rift and Ongamo populations. Their expansion transformed an earlier landscape in which East Rift communities were restricted to the highlands and Ongamo controlled much of the surrounding plains.

Four broad sets of communities emerged from the initial dispersal. Three remained on Kilimanjaro: the West Wachagga on the southern side, the Central Wachagga near modern Moshi, and the Rombo on the eastern side. The early Wagweno emerged in North Pare, while continued expansion eventually divided the Rombo into several communities and carried some West Wachagga immigrants into the forests of nearby Mount Meru.