Ashoura is marked on the tenth day of Muharram, the first month of the Islamic calendar, by all Muslims.
It is a particularly important period of mourning for Shia Muslims, as it marks the anniversary of the 7th century Battle of Karbala in present day Iraq, when Imam Hussein, grandson of Prophet Muhammad, was killed.
The death of Imam al-Hussein is considered by the Shia community as a symbol of humanity's struggle against injustice, tyranny and oppression.
The primary rituals and observances on Ashoura consist of public expressions of mourning. Sunni Muslims commemorate the day through voluntary fasting.
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.