It is regarded by Shia Muslims as the culmination of Muharram and the martyrdom of Husayn ibn Ali (the Prophet Muhammad's grandson) at the Battle of Karbala.
For Sunnis, Ashura commemorates the day Moses fasted to express his thankfulness for the Israelites' emancipation.
Today is also a Shia Muslim holy day of sorrow, which is commemorated by the majority of Shia Muslims. Other Muslim sects fast and meditate during the day.
Following Husayn's martyrdom, a white horse is paraded through the streets, signifying Husayn's horse returning to camp without a rider.
On the day of Ashura, Shia Muslims from all over the world travel to Iraq to visit the shrines of Husayn and his brother Abbas. The day is a sombre one in Islamic history, with Muslims commemorating Husayn's death at the Battle of Karbala.
The day is also a sad one for Sunni Muslims, who fast and give prayers to express their respects. Sermons are preached, and Husayn's life and principles are retold. The battle's history and tragedy are reenacted, and passion plays are performed. Self-flagellation is also practised by certain devout adherents. Men and women wear black on this day of grief since it is a day of mourning.
Shia Muslims wear mourning clothing on this day, and some make pilgrimages to the shrine in Karbala, Iraq. Offering homage and grieving Husayn's death are among the observances. During this difficult time, parties, music, and weddings are prohibited.
Ashura is a fasting day for Sunni Muslims to express appreciation for God's victory over Moses. It recalls the day when Allah parted the Red Sea to save Moses and his companions.