The following encyclopedias are excellent sources to learn more about the history of Christianity in the Mediterranean region in late antiquity and the early medieval period.
Covering the first eight centuries of the Christian church, this encyclopedia includes articles on such topics as the culture, doctrine, ecclesiology, history, philosophy, and theology of early Christianity.
Surveying the first six centuries of Christian history, this encyclopedia provides articles that explore theological and historical issues, including doctrines, practices, liturgy, heresies, and schisms.
This encyclopedia contains a wealth of information on heresies in the Western world from the time of Christ to the twentieth century, with over 600 entries devoted to the heretical traditions, individual heretics, heretical texts, religious sects, and much more.