Following an unsuccessful attempt on the life of the Shah of Iran in 1852, carried out by a small group of Babis acting without wider community sanction, Baha'u'llah, already a prominent follower of the Bab from a distinguished Iranian family, was arrested and imprisoned in Tehran's Siyah-Chal, the Black Pit, an underground dungeon converted from a former reservoir and known for its extremely harsh conditions, overcrowding and darkness.
Baha'u'llah later described, in his own writings, experiencing a profound spiritual revelation during this imprisonment, in which he described receiving a vision of a heavenly maiden who conveyed to him the beginning of his prophetic mission and the nature of the message he would eventually be called to deliver. He was held in the Siyah-Chal for approximately four months before being released, stripped of his property and banished from Iran, beginning a period of exile that would take him first to Baghdad and eventually to further destinations across the Ottoman empire over the following decades.
Baha'u'llah did not speak publicly of the revelation he described experiencing in the Siyah-Chal for over a decade afterward, continuing instead to live and act as a follower of the Bab's teaching during the intervening Baghdad period.