The Gods of Light and Darkness
Michael Grant describes how, during the Roman and Byzantine ages, the co-existence of good and evil in the world led to a variety of dualist religious beliefs.
Throughout the Roman Empire, as in our own times, millions of people were tormented by the eternally topical problem: why does evil exist? Surely, they felt, if the world was created and is controlled by a single allpowerful and beneficent deity (or pair or trinity or pantheon) such manifest and abundant evil would never be. Its survival and proliferation could, therefore, only be explained by the existence of two powers; not only a good one, but an evil one which must have created this world.