This book is a radical reinterpretation on the entire Mithraic Mythos. Rather than viewing Mithras as an imported Hellenized recast of the Middle Eastern Mithras (i.e., as an earlier form of what happened with Christianity), Ulansey posits that Mithras is an indigenous deity who was later conflated with Mithras. Reconciling the Unconquered Sun with the Conquered Sun of Helios, Ulansey posits that Mithras came about as the invisible sun around which the newly discovered migration of the "fixed" stars revolved. Fascinating material, and seemingly more explanative of the ties between Mithraism & other Initiative Secret Orders.

The teachings of the ancient Roman 'mystery religion' of Mithraism--one of the most important competitors of early Christianity--were guarded with the utmost secrecy, reveled only to select initiates. While the Mithraists never wrote down their secret doctrines, they did leave a key to them in the arcane iconography which filled the walls of their underground temples. Until now, all attempts to decipher this iconography have proven fruitless. Most experts have been content with a vague hypothesis that these images somehow derived from ancient Iranian religion.

He also has a web site with supplemental information.

This book is the book on Mithraism. Franz Cumont and his theories on the origins of Mithraism have dominated the field. If anyone was talking about Mithras between 1900-1990, odds are that they were utilizing Cumont as a resouce. While I prefer the theories extended by Ulansey above, Cumont's material is still relevent, as it details the Mithraic mysteries as they were extant (or as best can be reconstructed) in the Roman Empire until eradicated by Christianity.

The colorful Mithraic religion originated in Persia, enjoyed enormous popularity in Europe, and was ultimately destroyed by Christianity. This definitive treatment of Mithra by a leading authority on classical religions pieces together its mysteries: the principle characteristics of the god Mithra, the rituals, the teachings, the liturgy and much more. With 70 illustrations.