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
History of the Yoruba people little other than the displays of royal wealth. Most of the city states were controlled by "Obas", elected priestly monarchs, and councils made up of "Oloyes", recognised leaders of royal, noble, and often even common descent, who joined them in ruling over the kingdoms through a series of guilds and cults. Different states saw differing ratios of power between the kingship and the chiefs' council. Some, such as Oyo, had powerful, autocratic monarchs with almost total control, while in others such as the Ijebu city-states, the senatorial councils were supreme and the Ọba served as something of a figurehead. In