|During Ashoura, the Shia commemorate the death
of al-Hussein at the battle of Karbala [AFP]
Ashoura is marked on the tenth day of Muharram, the first month of the Islamic calendar, by all Muslims.
It marks the day Nuh (Noah) left the Ark and the day Musa (Moses) was saved from the Pharaoh of Egypt by God.
But for the Shia it is also a major religious festival to commemorate the martyrdom of al-Hussein, the grandson of the Prophet Muhammad, who died at the Battle of Karbala in AD 680.
The Prophet Muhammad used to fast on Ashoura in Mecca, where it became a common tradition for the early Muslims.
Every year since then, many Shia mark Ashoura by performing a pilgrimage to the mausoleum of Imam al-Hussein, which is traditionally held to be his tomb in Karbala.
Sunni Muslims commemorate the day through voluntary fasting.
Battle of Karbala
In early Islamic history some Muslims supported Ali, cousin of the Prophet and the fourth caliph (temporal and spiritual ruler) of the Muslim community.
Their support was based on the wish that the caliphate should stay within the Prophet's family.
They were called Shia, which means "the supporters" in Arabic.
Ali was murdered in AD 661 and his leading opponent Muawiya bin Abi Sufiyan became caliph.
Muawiya was succeeded by his son Yazid. Ali's son al-Hussein refused to accept Yazid's legitimacy and fighting between the two broke out.
Al-Hussein, accompanied by his family and a few fighters, faced Yazid's army.
A defiant al-Hussein refused to surrender even though he realised he was outnumbered.
After a brief battle, he and his followers were killed.
The primary rituals and observances on Ashoura consist of public expressions of mourning.
Some in the Shia community resort to flagellating themselves with chains and the blunt ends of swords. This is intended to exemplify the suffering Imam al-Hussein experienced shortly before his beheading.
The death of Imam al-Hussein is considered by the Shia community as a symbol of humanity's struggle against injustice, tyranny and oppression.
However, in recent years, some Shia clerics have been discouraging the bloodletting, saying it creates a backward and negative image of their community. Such leaders encourage people to donate blood to patients in need.
Many Iraqis cook throughout the night and offer meals of rice with meat and chickpeas to the pilgrims attending the ceremonies.