Millions of Muslims from across the world are marching toward the Iraqi holy city of Karbala to perform the rituals of Arba’een, one of the most revered religious occasions on the Islamic calendar.

Arba’een marks 40 days since Ashura when Imam Hussein, the grandson of Prophet Muhammad, was martyred in the desert plains of Karbala along with his 72 companions 14 centuries ago.

There are instantaneous enacting of the Karbala event. This scene purports to recount the forced displacement of Imam Hussein's family to Sham (the present day Syria) by the army of Yazid. (Photo by IRNA)

Monday will mark the final day of the mourning for Imam Hussein who was martyred in a battle with the massive army of Yazid I after refusing allegiance to the tyrant caliph.

Two pilgrims sit in a muse by the Euphrates River where the army of Yazid cut the way to Imam Hussein and his family to deny them water. (Photo by IRNA)

Each year, Sunni Muslims and followers of other religious groups such as Christians join the journey to mourn the martyrdom of Imam Hussein, the third Imam of Shia Muslims.

Pilgrims pass by palm orchards in Iraq. The palm tree has found an iconic significance and is associated with the event of Karbala. (Photo by IRNA)

The occasion has found additional significance in recent years as it has become a rallying cry for the campaign against Takfiri terrorists who have frequently targeted the pilgrims.

Charity practice is in full swing. At this makeshift bakery, fresh bread is handed out to the pilgrims who are heading to Karbala. (Photo by IRNA)

For the past few days, hundreds of thousands from Iraq, Pakistan, India, Iran, Bahrain, Saudi Arabia, Lebanon, Azerbaijan, Turkey and elsewhere have been trekking a main road between Najaf - another holy city in Iraq - and Karbala on foot to show their devotion.

Entire families on the move. These children are having a ride on their carriages. (Photo by IRNA)

Some of them started their hiking across the border in Iran and other countries.

On Iran's Mehran border with Iraq, a massive crowd awaited permit for entry after Iraqi authorities closed the crossing because they said they were overwhelmed.

Iranian pilgrims at the Mehran border crossing where they are awaiting permit to enter Iraq (Photo by IRNA)

According to officials, as many as two million Iranians are heading to Karbala which is expected to draw 20 million pilgrims by Sunday.

Their devotion doesn't fail them. These Iranian women have just arrived in Mehran to cross the border into Iraq.

Iraqi troops have been deployed to ensure security for the pilgrims. The northern and western parts of Iraq have been plagued by gruesome violence ever since Daesh terrorists began a campaign of terror in the country in June 2014.

A shot with security forces on the Najaf-Karbala road. These security men have put their lives on the line as have the pilgrims in the face of the marauding Takfiri terrorists.

The terrorist campaign, however, has not dissuaded pilgrims from around the world from making the journey.