Arbaeen is one of the most important ceremonies in the Shi’ite Muslim calendar. 

Arbaeen means forty in Arabic as forty days is the traditional length of mourning after the death of a family member or loved one in Muslim traditions. 

Imam Hussein was killed at the Battle of Karbala in central Iraq on 10 October 680 AD. 

Hussein was seen by his followers as the rightful heir of the prophet’s legacy. When he refused to pledge allegiance to the Umayyad caliphate, he was killed in the battle, cementing the schism between Sunni and Shiite Islam. Hussein’s half-brother Abbas was also killed in the battle. 

Millions of pilgrims will gather in Karbala on Arbaeen, making it the world’s largest annual human gathering. Making the pilgrimage, known in Arabic as the Ziara, many of the pilgrims travel barefooted from across Iraq and more than 50 countries. Over three million Iranians travel to Iraq for the Ziara. 

In Iran, thousands in Tehran will march to a town south of the capital to mourn at the shrine of Shiite saint Abdul Azim. #Arbaeen