At the mosque of Jamkaran, 110km south of Tehran and just east of the holy city of Qom, tens of thousands gather on Tuesdays to pray and drop messages for the "missing" imam into a well.

Abul-Qassem Mohammed, the 12th leader whom Shia Muslims regard as a successor to the prophet Mohammed, entered "occultation" in 941 and will one day return to rule justly before Judgment Day.