Despite the Islamic invasion of Egypt and the establishment of the Fatimid dynasty there in the late 600s AD, Nubia stayed Christian. In 641, the Fatimids made a treaty with Nubia that allowed Nubians to cross Egypt to get to Jerusalem on pilgrimages, and set up a trade where the Nubians sold slaves to Egypt and bought wheat, wine, and cloth. This treaty was kept up for more than five hundred years.
The rock-cut church of Lalibella
Meanwhile, the Eastern Roman Empire worked hard to keep up a relationship with Aksum, to keep the Abbasids and Fatimids from totally controlling African trade. In Aksum, the kings and bishops spoke Greek, and wore Byzantine clothing. Aksumite traders sold ivory to Roman traders, and bought Byzantine jewelry and glass. Many Christian churches were cut into the local sandstone, and painted with religious scenes. But by the 1200s AD, with the collapse of the Fatimids in Egypt, and the weakening of the Eastern Roman Empire, Aksum also weakened. Arab nomad tribes invaded over and over. Finally, just after 1300 AD, Aksum got its first Islamic king, and the many churches were all turned into mosques.
The Ancient African Kingdom of Kush (Cultures of the Past) by Pamela F. Service (1998)
A Place in the Sun, by Jill Rubalcaba (1998)
The Nubians: People of the Ancient Nile, by Bob Bianchi (1994)
Daily Life of the Nubians, by Bob Bianchi (2004)