Roman Catholic teachings on heresy first began in 380 AD with the Edict of Thessalonica. Later in the thirteenth century heresy was defined by Thomas Aquinas as "a species of infidelity in men who, having professed the faith of Christ, corrupt its dogmas." The Catholic Church asserts and teaches that its doctrines are the authoritative understandings of the faith taught by Christ and that the Holy Spirit protects the Church from falling into error when teaching these doctrines. To deny one or more of those doctrines, therefore, is to deny the faith of Christ. Heresy is both the non orthodox belief itself, and the act of holding to that belief.