Oyo Empire metropolitan Oyo. This may have been fine in the 15th century when Oyo controlled only its heartland. But to make and maintain farther conquest, the structure underwent several changes. Oyo maintained a semi-standing army of specialist cavalry soldiers called the "Eso", the "Esho" or, formally, the Eso of Ikoyi. These were 70 junior war chiefs who were nominated by the Oyo Mesi and confirmed by the Alaafin of Oyo. The Eso were appointed for their military skill without regard to heritage and were led by the Are-Ona-Kakanfo. After Oyo's return from exile, the post of Are-Ona-Kakanfo was established as the
Oyo Empire moved further south, to Ago d'Oyo. Oba Atiba sought to preserve what remained of Oyo by placing on Ibadan the duty of protecting the capital from the Ilorin in the north and northeast. He also attempted to get the Ijaye to protect Oyo from the west against the Dahomeans. The center of Yoruba power moved further south to Ibadan, a Yoruba war camp settled by Oyo commanders in 1830. Atiba's gambit failed, and Oyo never regained its prominence in the region. Oba Atiba otherwise called Atiba Atobatele died in 1859; His son Adeyemi I and the 3rd Alaafin to rule