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 Ajele. These were agents appointed by the Alaafin of Oyo to oversee his interest and monitor commerce. The lead representative of Oyo in the corridor was the Olu, ruler of the town of Ilaro. Ajaland was the last layer added to the empire. It was the most restive and distant, and kept in line with threats of expeditions against it. This territory extended from the non-Yoruba areas west of the Egbado Corridor far into Ewe controlled territory in modern Togo. This area, like all tributary states, was allowed a fair degree of autonomy as along as taxes were paid, the