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
Islam in Nigeria built in Ọyọ-Ile in AD 1550 although, there were no Yoruba Muslims, the Mosque only served the spiritual needs of foreign Muslims living in Ọyọ. Progressively, Islam came to Yoruba land, and Muslims started building Mosques: Iwo town led, its first Mosque built in 1655 followed by Iṣẹyin, in 1760; Lagos, 1774; Ṣaki, 1790; and Oṣogbo, 1889. In time, Islam spread to other towns like Oyo (the first Oyo convert was Solagberu), Ibadan, Abẹokuta, Ijẹbu-Ode, Ikirun, and Ẹdẹ before the 18th century Sokoto jihad. Several factors contributed to the rise of Islam in Yoruba land by mid 19th century. Before