Over 21 million Shia Muslims participated in this year’s Arbaeen pilgrimage in Iraq, marking the 40th day of mourning for the martyrdom of Imam Hussein, the grandson of the Prophet Muhammad and a central figure in Shia Islam. The event reached its peak on Sunday as attendees demonstrated support for Gaza.

Arbaeen, which means “40” in Arabic, is one of the largest religious gatherings in the world and a significant event for Shia Muslims, who are the majority in both Iraq and Iran. Karbala, where Hussein and his brother Abbas are buried in two large mausoleums, serves as the epicenter of the Shia Muslim world during this time.

Pilgrims openly express their grief, weeping and lamenting in memory of Hussein, who was killed in 680 AD during a battle in Karbala against the Umayyad Caliph Yazid. This year’s events have been marked by strong expressions of support for Palestine, with pilgrims waving Palestinian flags amidst the ongoing conflict in Gaza.

According to an official count from the institution that manages the Abbas mausoleum, the total number of Arbaeen pilgrims reached 21,480,525. Among them were approximately 3.5 million Iranian pilgrims, according to official figures reported from Tehran.

Mohammed al-Tamimi, a 32-year-old pilgrim, stated to AFP that the Palestinian flags waved among the worshippers were “to support our brothers in Palestine and in response to the Zionists, emphasizing that Muslims stand together against Zionist actions and the crimes occurring in Gaza.”

Since October, Israel has killed more than 40,000 Palestinians in Gaza. Estimates suggest that 1,139 people were killed during a Hamas-led attack in southern Israel on October 7. The Arbaeen celebrations, which always take place under strict security conditions, attracted around 22 million pilgrims last year, with Iran contributing the majority of foreign visitors, totaling 4 million.