Every chapter of Iraq's modern history can be seen in this great, sprawling city of the dead, its mausoleums stretching across the horizon from one of Shiite Islam's holiest shrines. And now, its sandy expanse grows again with the war dead killed by the country's latest adversary, the extremists of the Islamic State group.

"I expect that these graveyards will be expanded as more fighting against Daesh looms in the horizon," said Ali Abdul-Aali, the city official in charge of Najaf cemetery, using an Arabic acronym for the group.

Kings, scientists, artists, warriors and millions of others have a final resting place at Wadi al-Salam, or the "Valley of Peace" in Arabic, buried one atop the other in one of the world's largest cemeteries. The roughly 10-square-kilometer graveyard radiates out from the tomb of Imam Ali, the cousin and son-in-law of the Prophet Muhammad and Shiite Islam's most sacred martyr.

In its narrow rows, a visitor can find those killed in Iraq's long war in the 1980s with Iran or those slain in the sectarian bloodletting that followed the US-led invasion of the country in 2003.

In recent months, the growth of areas set aside for Shiite militias fighting the Islamic State group has been easy to see.

In the cemetery, one new section is for the Iranian-backed Hezbollah brigades, which is separate from the Lebanese group of the same name. Three tombs belong to an uncle and his nephews who took up arms on their own in June. They died three days later in a bomb blast in Jurf al-Sakhar, south of Baghdad.

At a separate section for the Shiite militia Asaib ahl al-Haq, or "the People of Righteousness", militiaman Ahmed Sabah Hassan washed the grave of his brother, Nouri, with rose water. Hassan said his brother was killed along with five other fighters when a suicide car bomb hit their vehicle in mid-March near Tikrit.

A picture of Hassan's brother, surrounded by artificial red and yellow flowers, stands on his tomb, along with his inscribed name and the date of his death. Miniature Iraqi flags waved around it in the dusty wind.

Before saying goodbye to his dead brother, Hassan vowed to return to Tikrit to continue the fight.