Karbala: history's long shadow
It is a privilege to do this work. I kept thinking that as we travelled along the road from Baghdad, to the city of Karbala.
Just like Bethlehem and Nazareth for Christians, Karbala is one of those places Muslim children hear about from when they are very young.
For many it takes on a mythical, unreachable status.
But here we were pulling up to the main security checkpoint of Karbala, being asked to park to the side while our papers were checked.
Many pilgrims were going through on foot.
As we carried on, the gold dome of the Imam Hussein mosque rose from the centre of the city, and soon we found ourselves standing at one of its many ornate doorways.
I watched a little girl pull back her mother by the hand and chastise her for not having kissed the entrance in respect.
Her mother dutifully spent a moment pressing her lips against the huge wooden doors to the mosque, before going inside.
In the vast prayer hall with its gold and marble, its huge chandeliers and its intricate blue and white tiling, was an incongruous red neon sign.
It marks the spot where it is believed Hussein, the grandson of the Prophet Muhammad, was beheaded.
The area on which the mosque complex is built is thought to be the site of the Battle of Karbala, in which not only Hussein, but 72 followers and members of his family, including his infant son, were slaughtered.
When you see Shia Muslims, bloodied, whipping themselves in their annual processions, they are commemorating the events that took place in Karbala.
Because while Muhammad's grandson is revered by all Muslim sects, it is Shias who trace their beliefs directly to his teachings.
The Shrine of Hussein, in the centre of the mosque, is now circled by a constant stream of pilgrims; kissing the marble, praying, often shedding tears. For Shias, the shrine represents the greatest tribute to martyrdom.
That battle of Karbala, in the 7th Century, in which Hussein was killed, is often cited as the moment Shia and Sunni Muslims were cleaved apart.
But Friday prayers in the Imam Hussein mosque looked almost the same as prayers in a Sunni mosque.
There are small differences in the rituals: at one point, for example, instead of crossing their hands over their stomachs, the lines of Shia devotees kept their hands by their sides.
But there is difference enough, it seems, that even to this day, some feel the need to continue the slaughter.
Over the last weeks, Iraqis have witnessed the kind of sectarian violence they had hoped was a thing of the past.
On one morning eight bombs went off in an hour in Shia districts of Baghdad. On another there were 11 almost simultaneously - again in Shia neighbourhoods.
There was an attack too on a Sunni mosque in Baqubah and another close to a funeral procession.
Speaking to Iraqis at the bombsites and in hospitals, what surprised me was the very apparent lack of hatred towards the other sect.
Instead, there appeared to be resigned consensus that Iraq's politicians were exploiting sectarian differences for their own gains - but that so too, were foreign powers.
It is something that has created a huge Sunni-Shia rift across the region: Iran the big power on one side; Saudi Arabia and Qatar on the other.
Other countries in the Middle East with mixed populations are feeling the effects, as Sunni and Shia groups within them start to align in what many now see as a holy war.
In Iraq, the links between Sunni militant groups, like al-Qaeda, and the fighting across the border in Syria have been much talked about.
But a couple of days before going to Karbala, we met a man who was involved in recruiting Shia fighters to go to Syria too: to fight not with the opposition, but alongside President Assad's forces.
"When somebody attacks your beliefs," he told me, "you have to defend them."
And where, I asked, are the Shia fighters going in Syria? His answer took us right back to Karbala.
He said their main aim was to defend the shrine of Zainab, another of the Prophet Muhammad's grandchildren, whose brother and two children were among those killed in the battle of Karbala.
After which, Shia believe, she was taken to Damascus, where she later died.
Sunnis disagree and think she was buried elsewhere, and in recent months there have been many reports of attempts to attack the Shia shrine.
The fighter told me they would keep laying down their lives until the shrine of Zainab was safe.
As I left the mosque in Karbala, with the traditional memento of a small amount of earth from the grounds, it was hard not to reflect on the way an event there 1,400 years ago was shaping the world today.