The Cathars: The Most Successful Heresy of the Middle Ages
Scripture, Creed, Theology: Lectures on the History of Christian Doctrine in the First Centuries
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This gave scholars access to many texts which were in wide circulation amongst early Christians, but which were deliberately excluded from the canon of the New Testament — gospels attributed to Thomas and Philip, texts recording the acts of Peter and the 12 disciples, apocalypses attributed to Paul and James, and so on.