Shiite Muslims perform with fire during Ashura commemorations in Najaf, Iraq. (Alaa Al-Marjani/Reuters)

Ashura, which means “Day of Remembrance,” is one of the most sacred and emotional events in Islam, a defining religious moment for Shiites. It marks the anniversary of the death of Imam Hussein, a grandson of the prophet Muhammad who was killed in battle, along with 72 followers and family members, in the 7th century in Karbala, a city in present-day Iraq.

It is observed each year across the Muslim world on the 10th day of Muharram, the first month of the Islamic year, and is a public holiday in Iran, Iraq, Afghanistan, Pakistan and other countries with large Shiite populations.

The events and rituals surrounding Ashura are colorful and dramatic, with huge banners hung from poles, black-draped archways erected across roadways, vivid posters depicting the life and death of Hussein, and martial dirges blaring from loudspeakers in hypnotic, pounding rhythms.

Emotional and religious fervor build throughout the day, leading to the bloody and controversial ritual in which groups of Shiite men and boys flagellate themselves with small knives and chains, and many others beat their chests for hours.

The defeat and death of Hussein, at the hands of forces loyal to Yazid, a caliph from the Arab Omayyad dynasty, was the seminal event that led to the division of Islam into Sunni and Shiite sects, with the major difference relating to the line of succession after the death of the prophet and lesser differences over issues of ritual and prayer. That split has come to divide the Middle East into camps dominated by Shiite Iran and Sunni Saudi Arabia, and it has led to sectarian violence in countries such as Iraq and Pakistan. Sunnis also observe Ashura, but as a day of gratitude and fasting in honor of the prophet Moses, rather than a day of sorrow and public mourning for Hussein.

Here's how nations around the world mark Ashura:

(Editor’s note: Some images in this post may be disturbing because of their violent or graphic nature.)

PAKISTAN


A Shiite Muslim boy flagellates himself with knives attached to chains to mark Ashura in Karachi. (Shakil Adil/AP)

Shiite Muslims beat their chests in a mourning ritual to commemorate Ashura in Quetta, Pakistan. (Arshad Butt/AP)

Pakistani Shiite Muslims flagellate themselves with knives during Ashura commemorations in Karachi. (Shakil Adil/AP)

IRAQ


Shiite Muslims perform with fire during Ashura commemorations in Najaf, Iraq. (Alaa Al-Marjani/Reuters)

Shiite Muslims gather during Ashura commemorations in Najaf, Iraq. (Alaa Al-Marjani/Reuters)

IRAN


Shiite Muslims re-enact events of Ashura in Tehran. (Vahid Salemi/AP)

The events of Ashura are reenacted in southern Tehran. (Vahid Salemi/AP)

A Shiite Muslim covers herself in mud during Ashura rituals in the city of Khorramabad, Iran. (Ebrahim Noroozi/AP)

AFGHANISTAN 


Shiite Muslims beat themselves with knives attached to chains during Ashura commemorations in Kabul. (Rahmat Gul/AP)

Knife sharpeners in Kabul hone the blades of small knives that are attached to chains and used in ritual self-flagellations by men and boys as part of Ashura commemorations. (Pamela Constable/The Washington Post)

An Afghan man sweeps blood after Shiite Muslim men beat themselves with knives attached to chains during a procession to mark Ashura in Kabul. (Rahmat Gul/AP)

(Pamela Constable/The Washington Post)

Mohammed Reza, 56, a Shiite Muslim, brought his two grandchildren to events marking Ashura in Kabul. (Pamela Constable/The Washington Post)

Yemen


Women loyal to Shiite rebels, known as Houthis, join Ashura commemorations in Sanaa, Yemen. (Hani Mohammed/AP)

Yemeni Shiite rebels, known as Houthis, mark the holy day of Ashura. (Hani Mohammed/AP)

Lebanon


A Shiite supporter of the Iranian-backed Hezbollah group listens to the story of Imam Hussein on the holy day of Ashura in a southern suburb of Beirut. (Hussein Malla/AP)

Shiite Muslims gash their foreheads with swords during a religious procession to mark Ashura in Nabatieh, Lebanon. (Ali Hashisho/Reuters)

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