In 615, some of Muhammad's followers emigrated to the Ethiopian Kingdom of Aksum and founded a small colony under the protection of the Christian Ethiopian emperor Aṣḥama ibn Abjar. Ibn Sa'ad mentions two separate migrations. According to him, most of the Muslims returned to Mecca prior to Hijra, while a second group rejoined them in Medina. Ibn Hisham and Tabari, however, only talk about one migration to Ethiopia. These accounts agree that Meccan persecution played a major role in Muhammad's decision to suggest that a number of his followers seek refuge among the Christians in Abyssinia. According to the famous letter of ʿUrwa preserved in al-Tabari, the majority of Muslims returned to their native town as Islam gained strength and high ranking Meccans, such as Umar and Hamzah converted.