By James Shaw
BBC News, Baghdad
The road south out of Baghdad is crammed with vehicles.
Crowds have been flocking to Karbala
Pick-up trucks with young men in the back waving red, green and yellow flags. Packed Japanese mini vans. Saloon cars carrying small squads of militiamen.
This is the road to Karbala: the road you take if you want to celebrate the festival of Shaabaniya, the birth of the Twelfth Imam, one of the main Imams in Shia Islam.
We flag down a bus to talk to some pilgrims.
As the side door slides open, a dozen faces look out eagerly. This is their chance to tell the world about their devotion to their religion.
Fear and anger
Are they afraid of attacks or ambushes by Sunni insurgents?
Iraqi army units surround Karbala ahead of the festival
"No," they insist, urgently and fiercely.
One young man's face is set in an expression which seems to combine fear and anger. He says they challenge the Takfiris, the Sunni extremists, to try to attack them.
"We follow the path of the Imam," he says. And that is a path which according to Shia tradition can lead to suffering, self-sacrifice and ultimately death.
These young men have only their religious fervour to protect them from the guns and bombs of the insurgents.
This is a religious celebration, so they travel without weapons. Nevertheless, the cars of discreetly armed men travelling near the pilgrims' buses are not there by chance.
They are probably militiamen from the Mahdi Army or another of the Shia armed groups. It is their job to fight off any attacks.
And there have been attacks. Mortars falling on the road north of Karbala have killed several pilgrims in the last few days.
A week ago, 14 Pakistanis and Indians were pulled off their bus and shot at the roadside.
This state of civil unrest might seem not much better than the lot of Shias under Saddam Hussein: often excluded from positions of power, prevented from practising their religion freely and killed in large numbers after a failed uprising in 1991.
But Jalaludin Saqhir, a Shia member of the Iraqi parliament and a well-known imam, claims the difference between then and now is like the difference between earth and heaven.
The Imam Hussein shrine lights up the night sky
Now ordinary Shias can fully express their religious faith. No terrorist tactic, he says, can stop them.
But he worries about the anger of Shias at the extremist Sunni groups who seem determined to stoke sectarian divisions. He fears an explosion of Shia anger against Sunnis that would tear the country apart.
This weekend, Karbala is surrounded by units of the Iraqi army, preventing vehicles from entering the town.
Police are on guard at every shrine.
But all this is no guarantee that insurgents will not attempt an attack. During these difficult days in Iraq, the fear of a bombing in the packed streets of a town like Karbala is something that no pilgrim can easily dismiss.