Hermias Sozomen’s , written in the fifth century, offers a vital and detailed account of the Christian Church’s transformation during the fourth century, spanning the reigns of Constantine to Theodosius I. This classic ecclesiastical history explores key theological controversies such as the Arian debate following the Council of Nicaea, while illuminating the roles of influential bishops, emperors, monks, and missionaries who shaped early Christianity. Sozomen’s work is particularly valued for its unique preservation of historical details and traditions not found in other sources, especially concerning monasticism. Presented here in a modernized English edition, the text maintains the original’s substance and character while updating spelling, punctuation, and formatting for contemporary readers. Whether approached by scholars, pastors, or history enthusiasts, this edition remains an indispensable resource for understanding the complex religious and political developments of late antiquity. This revision was prepared through an AI-assisted process, combining digital tools with traditional editorial work.