The ritual was commemorated on Sunday, the climax of a week-long pilgrimage where the faithful marched towards the Imam’s shrine in the northern district of Kadhimiyah.
The pilgrims were seen carrying a symbolic coffin of the Imam during the event.
The procession took place despite security threats. Shia religious events and sites are considered prime potential targets for attacks by the Daesh terrorist group.
The organizers estimate that more than six million people came to Kadhimiyah for the commemoration in recent days.
Ahmad Jamal, a 28-year-old civil servant in the crowd of pilgrims, said, "This visit means a lot to us. It is about showing respect for the suffering of the Imam and the injustice he faced and about reaffirming our dedication to him."
Tightened security measures have been in place across the capital to protect the pilgrims.
Many of the main thoroughfares have been blocked to traffic for days to minimize the risk of car bombs and allow the pilgrims to reach the shrine.
Gruesome violence has plagued parts of Iraq ever since Daesh terrorists mounted an offensive and took control of portions of the Iraqi territory in June 2014.
Iraqi army soldiers and allied fighters are leading operations to win back militant-held regions.