Islam was introduced to the northern Somali coast early on from the Arabian peninsula, shortly after the hijra. Zeila's two-mihrab Masjid al-Qiblatayn dates to the 7th century, and is the oldest mosque in Africa. In the late 9th century, Al-Yaqubi wrote that Muslims were living along the northern Somali seaboard. He also mentioned that the Adal kingdom had its capital in the city, suggesting that the Adal Sultanate with Zeila as its headquarters dates back to at least the 9th or 10th century. Adal's history from this founding period forth would be characterized by a succession of battles with neighbouring Abyssinia.