Pope Francis will visit the city of Najaf during his historic three-day trip to Iraq.
Najaf is home to Shiite Islam's most prominent hawza – an institution of religious learning, and Iraq's marja'iyya, the most learned and respected Shiite clerics in the country.
The city is revered by Shiites as the burial place of Imam Ali, described as a martyr, saint and would-be successor to the Prophet Mohammed. For this reason, Najaf is home of a gold-plated shrine, which has 35-metre tall golden minarets.
Other prominent marja'iyya reside mainly in Qom, Iran – some observers characterise the two cities as rival centres of Shiite religious authority.
This is largely because Najaf’s Shiite leaders – such as Grand Ayatollah Ali Al Sistani – are quietists who tend to avoid political statements, unlike their Iranian counterparts, who believe in religious rule.
Considered the most learned cleric in the Najaf hawza, Mr Al Sistani, the holiest figure for Shiite Iraqis and millions of Shiites around the world, is known as the "marja taqlid", or venerated object.
The pontiff will hold a private meeting with Mr Al Sistani, because the ayatollah seldom leaves his residence or makes public appearances, communicating with the public through a spokesman.
Pope Francis will meet Mr Al Sistani in his humble home, down a narrow alley in the ancient city, and while there may be photos of this trip, it is unlikely there will be more than one official image of the meeting.
Famous visitors to Najaf include Arabian explorer Ibn Battuta in the 14th century, who described the Imam Ali’s shrine as being “carpeted with various sorts of carpets of silk and other materials, and contains candelabra of gold and silver, large and small”.
So holy is the city for Shiites, millions have sought the distinction of being buried there.
Najaf has the world's largest cemetery, at the Wadi Al Salaam, or valley of peace.
As with much of Iraq, peace in Najaf has been far from assured in recent years.
After the US invasion of 2003, Iraq collapsed into chaos and the city was the focus of Al Qaeda-linked suicide bombers and Shiite militias fighting US forces.
Some of the attacks were near the shrine, including a car bomb in 2004 that killed more than 80 people.
Today, the area around the shrine is pedestrianised and visitors have to go through several checkpoints to enter, so Pope Francis can at least have peace of mind when he makes the journey to meet Mr Al Sistani.
