Najaf is renowned as the site of the Tomb of Alī ibn Abī Tālib also known as "Imām Alī" the First Imam of Shia's , the cousin and son-in-law of the prophet Muhammad whom the Shia consider to be the righteous caliph . The city is now a great center of pilgrimage from throughout the Shi'a Islamic world. It is estimated that only Mecca and Medina receive more Muslim pilgrims. As the burial site of Shia Islam's second most important figure, the Imam Ali Mosque is considered by Shias as the third holiest Islamic site.
The Imam Ali Mosque is housed in a grand structure with a gold gilded dome and many precious objects in the walls. Nearby is the Wadi-us-Salaam cemetery, reputed to be the largest in the world. It contains the tombs of several prophets and many of the devout from around the world aspire to be buried here, to be raised from the dead with Imām Alī on Judgement Day. Over the centuries, numerous hospices, schools, libraries and Sufi convents were built around the shrine to make the city the centre of Shīʻa learning and theology.
The Najaf seminary is one of the most important teaching centres in the Islamic world. Ayatollah Khomeini lectured there from 1964-1978. Many of the leading figures of the new Islamic movement that emerged in Iraq, Iran and Lebanon in the 1970s had studied at Najaf.
The Afghan city of Mazar-e Sharif also has a site which claims to be Ali's tomb and draws many pilgrims, but Najaf's claim is more widely accepted.