A 15-minute walk from the Iraqi border in the west Iranian town of Mehran, three young clerics are hard at work polishing the shoes of pilgrims.

Further down the road another cleric stands on a chair holding a Quran over the heads of passing crowds, blessing them as they march in the thousands towards the shrine of Hazrat Imam Hussain (AS) in Karbala, central Iraq.

A tailor is also working diligently, sewing up torn clothes for free.

And if anyone needs a money pouch, he can rustle one up from scratch in a matter of minutes.

These volunteers have been staying in Mehran for nearly two weeks, offering their services to the pilgrims as they walk towards the crossing.

Some 1.8 million Iranians have been given Iraqi visas to make the pilgrimage to Karbala for the holy festival of Arbaeen this year — and many will pass on foot through the border point at Mehran.

Arbaeen, which this year falls on October 30, marks 40 days after the martyrdom in 680 of Hazrat Imam Hussain (AS), grandson of the Prophet Muhammad (PBUH) who refused to accept the leadership of the "usurper" caliph Yazid and was massacred along with his followers at Karbala.

Most of the devout walk all or part of the way to the shrine, one of the holiest sites in Shia Islam.

But some forego the march to the shrine, and instead stop in Mehran for days or weeks to serve the pilgrims.

No higher reward

For the many hundreds of devout volunteers who run "mokebs" — tents that hand out free food and services —their work can feel even more sacred than the pilgrimage itself.

"There is no higher sawab (divine reward) than to serve on the path of the Imam," says Mohsen Mohebbi, a cleric from the holy city of Qom, busy polishing shoes.

"I mend torn clothes and backpacks, shorten chadors so that they don't become muddy on the road, and sew money pouches for the pilgrims," says Ali Nujuki, a 69-year-old retired tailor from Isfahan province who has been working here for two weeks with his wife and daughter.

"The joy of serving the pilgrims of Arbaeen is even greater than for the pilgrimage itself," he adds.

As well as huge numbers from Iran, many Shias are also passing through from neighbouring countries including Pakistan, Georgia and Azerbaijan.

"I don't care who is wearing the shoe I shine, what language they speak or what race they are," says Mohebbi.

"As long as they are marching towards Hazrat Imam Hussain (AS) I will kiss their feet."

The march was forbidden for many years under former Iraqi dictator Saddam Hussein, who fought a devastating war with Iran in the 1980's.

Restrictions were only lifted after his ouster in 2003.

With the formation of a new Iraqi state, where the post of prime minister is held by a Shia, the march quickly became one of the most popular pilgrimages in the world.

"This is a march of unity and solidarity among Shia and Sunni, Persian and Arab, people from all strata and walks of life," says Mohammad Taghi Ganji, a 46-year-old cleric from Semnan province.

"The cursed Saddam closed the path (to Hazrat Imam Hussain's (AS) shrine), but now look where he is, and Arbaeen is stronger than ever," adds Ganji, whose tent was staffed by volunteers from a local branch of Iran's Revolutionary Guards forces.

"Whenever enemies closed a door on us, Hazrat Imam Hussain (AS) himself opened another path for us."