Imam is a title given in Shiite Islam to someone who is the spiritual and political successor of the founder of Islam, Prophet Muhammad.
Imam Musa al-Kadhim lived in the 8th century in Iraq.
Iraqi Shiites mark the anniversary amid tightened security.
Iraqi Prime Minister Haider al-Abadi paid a visit to Baghdad Joint Operation on Friday to oversee the security arrangements put in place to safeguard the visitors to the holy shrine.
Shiite pilgrims previously have fallen victim to suicide bomb attacks in different parts of the country.
The extremist group ISIS especially targets the Shiite pilgrims, whom ISIS deems to be apostates, and therefore legitimate targets.
Credits: Photos from AFP