Iran’s former supreme leader, Ali Khamenei, who was killed in U.S.-Israeli airstrikes in February, will be buried on Thursday in the city of Mashhad, the final stop of a funeral procession that is expected to last six days and visit five cities.

Mashhad, a city of three million people in northeastern Iran, is the country’s second most populous city after Tehran and where Mr. Khamenei was born in 1939. Shiite Muslims revere it as Iran’s holiest city because of its close association with Imam Reza, one of twelve religious leaders considered by Shiites to be the spiritual heirs of the Prophet Muhammad.

According to Shiite teachings, Imam Reza was poisoned in a nearby village on the orders of a local ruler, known as a caliph, in the ninth century and buried in Mashhad, making him the only one of the 12 Shiite imams to be entombed in the country. The authorities say the mausoleum attracts millions of pilgrims each year.

According to Iranian officials, the complex of buildings making up the shrine, with its towering golden dome and intricate decorative tiles, dates to the ninth century.

By choosing to bury Ayatollah Khamenei in the complex, the Iranian authorities hope to emphasize his status as a religious leader, said Roham Alvandi, a professor of Iranian history at the London School of Economics.

“It is common for Persian monarchs to be buried in such holy shrines in Iran and Iraq, in proximity to the Shiite imams, much as medieval European monarchs were typically buried in cathedrals and abbeys,” he said.

On Thursday, a funeral procession will be held for Mr. Khamenei through the streets of Mashhad and to the complex, according to Iranian state media.

The route that the funeral will take from Tehran also goes through Iraqi cities that have Shiite shrines, which is notable, said Sajjad Rizvi, a professor of Islamic intellectual history at the University of Exeter, as it matches the stops increasingly favored for the funeral processions of Shiite Islam’s most revered leaders. He noted that when another high-ranking Shiite cleric, Ayatollah Sheikh Muhammad Ishaq al-Fayyad, passed away a few weeks ago, his funeral went to the same shrine cities.

“It’s significant that the funeral is taking this route because it’s making the claim that Mr. Khamenei was a leading religious figure like Sheikh al-Fayyad,” Mr. Rizvi said.

Mashhad is deeply intertwined with the Khameneis’ conservative brand of religious politics.

Mr. Khamenei’s son and successor as Iran’s supreme leader, Ayatollah Mojtaba Khamenei, was also born in the city. So was Ebrahim Raisi, Iran’s former president under the late Mr. Khamenei. Mr. Raisi was buried in the shrine of Imam Reza following his death in a helicopter crash in 2024.

Mashhad has also been a site of unrest, including in January, when anti-government protests swept across Iran. Large crowds in Mashhad chanted slogans against the government, and Iranian security forces conducted a brutal crackdown, according to video footage verified by The New York Times.

On Thursday, the government says it expects more than a million supporters of the regime to assemble in Mashhad to mourn Mr. Khamenei’s death.