Imam Husayn's martyrdom is a sad day for all Muslims especially the Shi'a, who mourn the massacre of their "Prince of Martyrs" and his family in Karbala in 61AH/680CE.
Imam Husayn held the title of Imam, meaning spiritual leader of Islam; and he refused to swear allegiance to Yazid, the second Umayyad Caliph. He tried to travel from Medina to Kufa but was surrounded by forces loyal to Yazid in the desert at a place now known as Karbala.
Imam Husayn's followers were greatly outnumbered and dying of thirst, indeed his brother 'Abbas was killed trying to bring water back to the camp. On the 10th day of Muharram, Imam Husayn's followers were massacred and their leader beheaded after declaring, "death with dignity is better than life with humiliation".
The commemoration of this brutal massacre begins on the first day of Muharram and continues for 40 days. During the first 10 days of Muharram millions of Shi'a (and Sunni) Muslims remember the massacre at Karbala and strive to feel some of Husayn's pain.
The 10th day of Muharram is known as 'Ahsura' which recalls the day of the massacre in Karbala, a town in modern day Iraq which is second only to Mecca and Najaf as a spiritual beacon to the Shi'a.
Just 100km south of Baghdad, Karbala houses the shrine of Imam Husayn and his brother Al-Abbas. For centuries Shi'a pilgrims flocked here during Muharram, a practice which was severely limited under the regime of Saddam Hussein.