The axum empire was one of the first places to produce illuminated manuscripts. these books spread christianity throughout the empire because they:

-Because those illuminated Manuscripts were frequently devoted in narrating biblical stories. At first , only the Royalties were required to study those books and manuscripts

-But later on, a lot of Missionaries and Evangelists were using those scripts to spread Christianity on the rest of the empire.

-Allowed illiterate citizens to understand the key points of the stories.