Thousands of Shia Muslims gather at the Imam Husayn Holy Shrine in Karbala, Iraq, on Sunday, July 6, to observe the Day of Ashura.

Many are seen dressed in black as a sign of mourning, crowding into the shrine and its surrounding areas.

Ashura, marked on the 10th day of Muharram—one of Islam’s holiest months—commemorates the martyrdom of Husayn Ibn Ali, the Prophet Muhammad’s grandson, who was killed along with 72 companions in the Battle of Karbala in 680 AD (61 AH).