The basis of Egyptian religion was "of a purely Nigritian character,"[58] and in its developed form Sudanese tribal gods were invoked and venerated by the priests. In Upper Egypt, near the confines of Ethiopia, paintings repeatedly represent black priests conferring on red Egyptian priests the instruments and symbols of priesthood. In the Sudan to-day Frobenius distinguishes four principal religions: first, earthly ancestor worship; next, the social cosmogony of the Atlantic races; third, the religion of the Bori, and fourth, Islam. The Bori religion spreads from Nubia as far as the Hausa, and from Lake Chad in the Niger as far as the Yoruba. It is the religion of possession and has been connected by some with Asiatic influences. From without have come two great religious influences, Islam and Christianity. Islam came by conquest, trade, and proselytism. As a conqueror it reached Egypt in the seventh century and had by the end of the fourteenth century firm footing in the Egyptian Sudan. It overran the central Sudan by the close of the seventeenth century, and at the beginning of the nineteenth century had swept over Senegambia and the whole valley of the Niger down to the Gulf of Guinea. On the east Islam approached as a trader in the eighth century; it spread into Somaliland and overran Nubia in the fourteenth century. To-day Islam dominates Africa north of ten degrees north latitude and is strong between five and ten degrees north latitude. In the east it reaches below the Victoria Nyanza. Christianity early entered Africa; indeed, as Mommsen says, "It was through Africa that Christianity became the religion of the world. Tertullian and Cyprian were from Carthage, Arnobius from Sicca Veneria, Lactantius, and probably in like manner Minucius Felix, in spite of their Latin names, were natives of Africa, and not less so Augustine. In Africa the Church found its most zealous confessors of the faith and its most gifted defenders."[59] The Africa referred to here, however, was not Negroland, but Africa above the desert, where Negro blood was represented in the ancient Mediterranean race and by intercourse across the desert. On the other hand Christianity was early represented in the valley of the Nile under "the most holy pope and patriarch of the great city of Alexandria and of all of the land of Egypt, of Jerusalem, the holy city, of Nubia, Abyssinia, and Pentapolis, and all the preaching of St. Mark." This patriarchate had a hundred bishoprics in the fourth century and included thousands of black Christians. Through it the Cross preceded the Crescent in some of the remotest parts of black Africa.