neighbors even without the backing of the main imperial army. These forces were often utilized in Oyo's distant campaigns on the coast or against other states. Culture Commerce Oyo became the southern emporium of the Trans-Saharan trade. Exchanges were made in salt, leather, horses, kola nuts, ivory, cloth and slaves. The Yoruba of metropolitan Oyo were also highly skilled in craft making and iron work. Aside from taxes on trade products coming in and out of the empire, Oyo also became wealthy off the taxes imposed on its tributaries. Taxes on the kingdom of Dahomey alone brought in an amount estimated at 1 million U.S. dollars a year. In pre colonial times, was a type of rotating savings and credit association among the Yoruba. Esusu was recorded to have been practiced in Oyo during the reign of Alaafin Abiodun in the 18th century. Architecture Potsherd Pavements at Old Oyo have been dated from the 13th to 14th centuries. Zenith By 1680, the Oyo Empire spanned over 150,000 square kilometers. It reached the height of its power in the 18th century. Despite its violent creation, it was held together by mutual self-interest. The government was able to provide unity for a vast area through a combination of local autonomy and imperial authority. Unlike the great savannah empires, of which Oyo may not be called a successor since it was a successor of Ife, there was little if any Islamic influence in the empire. It is known that at least some Muslim officials were kept in Metropolitan Oyo, and men capable of writing and calculating in Arabic were reported by French traders in 1787. Muslim communities existed in several towns throughout the empire by the 19th century. Decline Many believe the decline of the Oyo empire had started as early as 1754 with the dynastic intrigues and palace coups sponsored by the Oyo Prime Minister Gaha. Gaha, in his quest for absolute power, conspired with the Oyo Mesi and probably to some extent the Ogboni to force four successive Alaafins to commit ritual suicide after they had been presented with the symbolic parrot's eggs. Between June and October 1754 alone, two Alaafins had been forced to commit suicide by Gaha. Because of this, Alaafin Awonbioju spent 130 days on the throne, while Alaafin Labisi only spent 17 days on the throne. Gaha's treachery was not ended until 1774 during the reign of