as an introduction i would say the darkening age by catherine nixey. while i have my issues with the book, it's an easy read and covers the topic well enough. while not exactly focusing on the topic of persecutions i would also recommend the myth of persecutions by moss. it focuses on how the storys of martyrs were either exaggerated, made up and in some cases appropriated from pagans. currently i'm reading pic related. while it's a more scholarly work and a harder read i really like it this far.
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