Persia, Sheba, Nabataea and the Roman Empire. They used the ancient Somali maritime vessel known as the beden to transport their cargo. After the Roman conquest of the Nabataean Empire and the Roman naval presence at Aden to curb pillaging, Somali and Gulf Arab merchants by agreement barred Indian ships from trading in the free port cities of the Arabian peninsula to protect the interests of Somali and Arab merchants in the extremely lucrative ancient Red Sea–Mediterranean Sea commerce. However, Indian merchants continued to trade in the port cities of the Somali peninsula, which was free from Roman interference. For centuries, the Indian merchants brought large quantities of cinnamon from Sri Lanka and Indonesia to Somalia and Arabia. This is said to have been the best kept secret of the Somali and Gulf Arab merchants in their trade with the Roman and Greek world. The Romans and Greeks believed the source of cinnamon to have been the Somali peninsula, but in reality, the highly valued product was brought to Somalia by way of Indian ships. Through collusive agreement by Somali and Gulf Arab traders, Indian/Chinese cinnamon was also exported for far higher prices to North Africa, the Near East and Europe, which made the cinnamon trade a very profitable revenue generator, especially for the Somali merchants through whose hands large quantities were shipped across ancient sea and land routes. Medieval 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. Throughout the Middle Ages, Arab immigrants arrived in Somaliland, a historical experience which would later lead to the legendary stories about Muslim sheikhs such as Daarood and Ishaaq bin Ahmed (the purported ancestors of the Darod and Isaaq clans, respectively) travelling from Arabia to Somalia and marrying into the local Dir clan. The Sultanate of Mogadishu's first dynasty was established by Abubakr bin Fakhr ad-Din. This ruling house was