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
Yoruba people Africa. The historical Yoruba develop "in situ", out of earlier Mesolithic Volta-Niger populations, by the 1st millennium BCE. Oral history recorded under the Oyo Empire derives the Yoruba as an ethnic group from the population of the older kingdom of Ile-Ife. The Yoruba were the dominant cultural force in southern Nigeria as far back as the 11th century. The Yoruba are among the most urbanized people in Africa. For centuries before the arrival of the British colonial administration most Yoruba already lived in well structured urban centres organized around powerful city-states ("Ìlú") centred around the residence of the "Oba". In