Najaf is the clearest case anywhere of a settlement whose entire economy, scholarship and social structure grew out of a single burial. The grave of Ali ibn Abi Talib was, according to the tradition, kept secret for more than a century to protect it from desecration, and made public under the Abbasids. Everything else followed.
The hawza of Najaf is the senior seminary of Twelver Shia Islam, a network of teaching circles rather than a single institution, and the marjaiyya, the office of the senior scholars whose rulings the laity follow, has been seated there for most of its history. That gives a shrine city a governing role in a transnational religious community, and the political consequences have been considerable, from the tobacco protest of the 1890s to the interventions of the Najaf marjaiyya after 2003.
Beside the shrine lies Wadi al Salam, the valley of peace, which is generally described as the largest cemetery in the world, several square kilometres of tombs accumulated over centuries by people seeking burial near Ali. Bodies are still brought from across the region, and the transport, washing and burial of the dead is a substantial part of the city's working life.
Karbala, seventy kilometres away, holds two shrines facing one another across an open space, Husayn and his half brother Abbas, and the walk between them is itself an observance.
The other stations of the circuit are Kadhimiya in Baghdad, Samarra, where the shrine was bombed in 2006 with severe consequences for Iraq, Mashhad in Iran for the eighth imam, Qom for Fatima Masumeh, and the Baqi cemetery in Medina, where the mausolea of four imams were demolished and the ground is now unmarked.