Ashura is an important holiday in the Islamic calendar, marking the death of Husayn ibn Ali (Imam Hussein), a grandson of prophet Muhammad. He was killed in 680 AD in the Battle of Karbala which became a central event to Shia Islam. Since then, the first ten days of Muharram, the first month of the Islamic calendar, are a national holiday in Shia Islamic countries, with the tenth day culminating in Ashura.
The Ashura day of mourning in Karbala was the target of a terrorist attack in 2004, when simultaneous bombings in Karbala and Najaf killed 134 people. A 2005 stampede had occurred in Baghdad during a similar event, caused by word that the event might be subject to a terrorist bombing. More recently, several attacks on Ashura processions have been perpetrated by Sunni extremists.