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 17th century, Oyo took on a noticeably more militant character. The influence of an aggressive Yoruba culture is exemplified in the standards placed on the oba (king) and the roles of his council. The oba (meaning 'king' in the Yoruba language) at Oyo, who was referred to as the Alaafin of Oyo (Alaafin means 'owner of the palace' in Yoruba), was the head of the empire and supreme overlord of the people. He was responsible for keeping tributaries safe from attack, settling internal quarrels between sub-rulers, and mediating between those sub-rulers and their people. The Alaafin of Oyo was also