One of Ancient Rome's most intriguing pagan religions is that of the mysterious cult of Mithras: the celebration of an ancient Indo-Iranian god, who gained an enormous amount of popularity during the first several centuries of the Common Era. Mithraism, as the cult has been commonly termed, was a mystery religion, one whose nature and teachings remain somewhat secretive today, since the cult left no written works. Mithraism provides a particularly interesting point of view regarding the Roman Empire, since the cult began around the same time that Christianity did, but was entirely forgotten just over 400 years later. In analyzing why one religion succeeded while the other failed, this paper examines beliefs such as astrology, Zoroastrianism, monotheism, and fatalism within the context of life in the Roman Empire.