 In particular, in the early 10th century, the doctrine of the occultation, which declares that the Twelfth Imam did not die but was concealed by God from the eyes of men, was expounded.The Mahdi became synonymous with the "Hidden Imam" who was thought to be in occultation awaiting the time that God has ordered for his return.This return is envisaged as occurring shortly before the final Day of judgment.