In The Cult of Mithras in Late Antiquity David Walsh explores how the cult of Mithras developed across the 3rd and 4th centuries A.D. and why by the early 5th century the cult had completely disappeared. Contrary to the traditional narrative that the cult was violently persecuted out of existence by Christians, Walsh demonstrates that the cult's decline was a far more gradual process that resulted from a variety of factors. He also challenges the popular image of the cult as a monolithic entity, highlighting how by the 4th century Mithras had come to mean different things to different people in different places.
Great resource on Mithraism in the last centuries of its existence, a compacted, concise essence on many topics concerning Persianism with a focus on the Mithraea across its last centuries. The style of this writing is clear, unobstructive, and pleasant, the meritorical side of it - without fault. Before reading this work I was unaware that there was a Mithraeum in Saguntium (Caernarfon in Wales), I've visited the place to see the castle back in the uni-days, most unfortunately I missed the ruins of the fort and Mithraea.