Samarra: Shia pilgrimage centre

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The golden dome dominated the Samarra skyline
Over the centuries, the central Iraqi city of Samarra has attracted millions of Shia pilgrims from all over the Muslim world.
They travel to the city to worship at the sacred tombs of Ali al-Hadi and al-Hasan al-Askari, the 10th and 11th Shia Imams, and the site where the 12th Imam, Mohammed al-Mahdi, disappeared.
Imam al-Mahdi, known as the 'hidden Imam', was the son and grandson of the two previous imams, and Shias pray at the mosque for his return.
Shia Islam was led by imams, believed to be divinely appointed from the Prophet Muhammad's family, until the late 9th Century.
Sacred
Al-Hadi, the 10th Shia Imam, was born in Medina in modern-day Saudi Arabia in 827. He became Imam at the age of six.
In 848, he and his son were brought to Samarra, then the capital of the Abbasid Empire and placed under house arrest by the Caliph al-Mutawakkil.

It is believed Imam al-Hadi was poisoned in 868, and buried in a house near the original mosque of al-Mutasim.
Al-Askari succeeded his father as imam, but remained under house arrest until his death in 874. He was buried beside his father in what was later to become the al-Askari shrine.
In addition to the tombs of the two imams, are those of Hakima Khatun, the sister of Imam al-Hadi, and Narjis Khatun, the mother of Imam al-Mahdi.
The huge complex also contains a second shrine above the cave (sirdab), where the young Imam al-Mahdi, Al-Askari's son, was said to have been hidden before he disappeared in 878.
Shia Muslims believe he did not die and still await his return more than 1,100 years later.
Visitors descend stairs to enter the sirdab, which "