Lost Christianities by Bart Ehrman explores the immense diversity of early Christian beliefs during the second and third centuries, arguing that modern orthodoxy emerged only after "proto-orthodox" Christians won intense battles for scriptural authority. It highlights forgotten, "heretical" faiths—like Gnostics and Marcionites—who had their own gospels and interpretations. Ehrman aims to show that the history of early Christianity was shaped by political and intellectual conflicts, not just divine consensus.