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
Old Oyo National Park ancient political capital of Oyo Empire of the Yoruba people, and contains the ruins of this city. Oyo Ile was destroyed in the late 18th century by Ilorin and Hausa/Fulani warriors at the culmination of the rebellion of Afonja, commander of Oyo Empire's provincial army for which he allied himself with Hausa/Fulani Muslim jihadists. The national park originated in two earlier native administrative forest reserves, Upper Ogun established in 1936 and Oyo-lle established in 1941. These were converted to game reserves in 1952, then combined and upgraded to the present status of a national park. The park covers 2,512 km,