The Kikuyu share common historical roots with the Kamba, Embu, Mbere, Tharaka, and Meru. All of these groups date back to a prototype population known as the Thagicu. Migrating from the north, the Thagicu settled in the Mount Kenya region sometime between the twelfth and fourteenth centuries. As splinter groups formed, one of the groups migrated south and settled on the southwestern slopes of Kirinyaga (Mount Kenya). Archaeological evidence suggests that the people who settled there hunted game, herded sheep and goats, and worked with iron to make simple tools and weapons.
There were additional Bantu migrations from the north-east, followed by periods of settlement, intermarriage, and further splintering of the Thagicu in the fifteenth and sixteenth centuries. The Kikuyu trace their descent from one of the splinter groups that settled at the convergence of the Tana (Thagana) and Thika rivers. From the settlement at Ithanga, subgroups migrated in several directions, some north to Nyeri, others northeast to Kirinyaga, and some south to Murang'a over the next two centuries. Some migrated further south than Murang'a, toward Kiambu, in the eighteenth century, and came into contact with a hunting people they called the Aathi. They intermarried with the Aathi and acquired land from them in exchange for goats.
As different Kikuyu settled in different areas, a clan structure emerged. Each clan traced its descent back to a specific female ancestor. According to Kikuyu mythology, there were nine (or nine plus one) original clans. Two clans, the Acera and Agaciku, are thought to have formed through contact with neighboring Kamba. The largest clan is the Anjiru; its members were formerly renowned as great warriors and medicine men. The Aithaga clan was known for its ironworks, and its members were also thought to have the power to control rain. Other clans include the Ambui, Angari, Aithiegeni, Aithirandu, and Aithanga. According to Kikuyu myths, Kikuyu and Mumbi were the male and female progenitors of the nine clan ancestors.