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 Oyo Empire, usually the Alaafin's oldest son succeeded his father to the throne. But, this sometimes led to the oldest son, i.e. the first-born prince, the Aremo, hastening the death of his father. Independently of the possible succession, the Aremo was quite powerful in his own right. For instance, by custom, the Alaafin abstained from leaving the palace, except during the important festivals, which in practice curtailed his power. By contrast, the Aremo often left the palace. This led noted historian S. Johnson to observe: "The father is the king of the palace, and the son the King for the