Indications of the first baptismal endeavors in Nubia can be traced back to the apostolic period. The final baptism of all three Nubian states (Nobatia, Makuria, Alodia) took place in the 6th century. A strong and lasting alliance with Byzantium implied cultural, religious and trade contacts. The historiography is dominated by the theory of the collapse of Nubian- Byzantine ties after the Islamic Conquest of Egypt in the 7th century. The similarity of Nubian society with Byzantine after the seventh century is explained by the theory of memory of Byzantium in Nubia. On the other hand, relying on the Arab-Byzantine sources, the trade relations between Nubia and Byzantium can be traced back to the 10th century. According to Ibn Yahya the Nubians appear as a guard of emperors in Constantinople. The general Byzantine term of the Ethiopians mainly denoted various East African peoples in Byzantine sources. In the tenth century, it is possible to identify Nubians in such mentions.