It's not "a" mosque – it's "the" mosque

Imam 'Ali Mosque, An-Najaf, Iraq

The Imam ‘Ali mosque in An-Najaf, Iraq, is the holiest site in Shi’a Islam. It is named for the man whose tomb it houses – ‘Ali bin Abu Talib.

Why is ‘Ali significant?

‘Ali gained prominence following the death of the Prophet Muhammad, who left no male heirs, throwing the adherents to the new faith into disarray. Who would follow Muhammad as the leader of the faithful? The Arabic word for “one who follows or succeeds,” - khalifah (Caliph) - was adopted as the title.

Many believed that the successor to Muhammad should be a family member, someone in the bloodline of the Prophet. The people who favored the selection of ‘Ali as the caliph were called the Shi’at ‘Ali, the “partisans of ‘Ali,” and hence the name Shi’a.

The other school of thought, held by many prominent Muslims of the day, was that the caliph should be drawn from one of the senior and learned members of the faith, the ummah or “community.” These were the Sunnis, the traditionalists. The Sunni position prevailed and the first three caliphs were not of Muhammad’s bloodline.

The Shi’a declared ‘Ali as their first imam, in what would become known as the Twelver* school of Shi’a Islam. It was not until the deaths of the first three Sunni caliphs that ‘Ali was named to be the fourth caliph in 656. However, hopes for reconciliation between the Sunni and Shi’a were short-lived.

A power struggle for the caliphate ensued between ‘Ali, who had set up his office in Kufah (near An-Najaf, Iraq) and the Damascus-based ‘Umayyad dynasty. Although there was some fighting between supporters of the two factions, ‘Ali was assassinated in Kufah in 661. The shrine in An-Najaf was constructed to house his tomb.

The Shi’a named ‘Ali’s son Hasan to be next caliph (or the second imam), however, Hasan chose to abdicate his position in favor of the ‘Umayyads, the very people responsible for his father’s murder.

Hasan’s brother Husayn assumed the Shi’a imamate, becoming the third imam. This action sparked a civil war that created the major divide in Islamic history. In 680, Husayn was killed in battle against superior ‘Umayyad forces in Karbala’, Iraq on the tenth day of the month of Muharram. This day is commemorated by all Shi’a as ‘Ashura (literally, “the tenth”) as a day of mourning and perfidy on the part of the Sunnis. Husayn’s body is buried in the shrine at Karbala’, also a holy site for the Shi’a.

It’s not "a mosque" – it’s "the mosque."

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* These Shi’a believe that there were 12 imams. The Twelfth Imam is also known as the "hidden imam" who did not die, but entered a period of occultation. The imam, also called the mahdi, will return at the end of time.