As Iran prepares to bury the late Supreme Leader Ayatollah Ali Khamenei this weekend, the nation is bracing for an outpouring of grief that recalls another seismic moment in the country’s modern history — the funeral of Ayatollah Ruhollah Khomeini, whose 1989 burial drew an estimated 10.2 million people and descended into chaos that left mourners crushed and his own son injured.

On June 6, 1989, millions of Iranians poured into the streets of Tehran to bid farewell to the architect of the 1979 Islamic Revolution. What was meant to be a solemn procession quickly spiraled out of control as the sheer force of the grieving masses overwhelmed security forces and turned the event into one of the deadliest funerals in modern history.

The Associated Press, which was on the ground that day, documented a scene of unprecedented scale and pandemonium. Mourners beat their heads and chests rhythmically in the stifling 91-degree heat, their wails cutting through the air as they fought to get closer to the coffin. The crowd surged forward with such force that the hearse became stranded in a sea of black-clad bodies, unable to advance even a half-mile two hours into the procession.

At one point, the chaos turned dangerous. Mourners rushed the casket, and the 86-year-old religious leader’s white-wrapped body tumbled out into the crowd. Security forces fired into the air in a desperate attempt to disperse the multitudes, but the grieving masses refused to budge. Revolutionary Guards beat mourners on their hands to force them to release the coffin. According to initial reports, at least eight people were killed and some 11,000 others were injured in the frenzy.

Among those caught in the crush was Khomeini’s only son, Ahmad, 43, who was knocked down in a dusty north Tehran square outside the Mosalla Mosque, where his father’s body had lain in state since Monday in an air-conditioned glass-encased bier. Ahmad’s white turban fell off as he was hoisted above the crowd and passed from hand to hand to an ambulance at the edge of the square. He appeared pale and drowsy but conscious.

The funeral service itself was conducted by Ayatollah Mohammad-Reza Golpaygani, one of the four remaining senior ayatollahs in Iran at the time, who choked often and lifted his spectacles to wipe tears with a handkerchief. After the 30-minute ceremony, Khomeini’s body — wrapped in the Islamic republic flag and placed in a wooden coffin covered with a white cloth — was carried by Revolutionary Guards from hand to hand into a white van.

Crowds cried hysterically as readings from the Koran blared from the mosque’s minaret. “Farewell beloved imam!” and “Oh Khomeini, why have you left us?” they shouted, pounding their heads and chests with clenched fists in a traditional Shiite expression of grief. About 2 million frenzied mourners had kept a nightlong candle-lit vigil around the bier. Some scratched their faces until the blood ran and threw ashes over their clothes. Firefighters sprayed the crowds with water to cool them off.

The chaos forced authorities to postpone the burial, as Islam forbids burying the dead after nightfall. Tehran television said it was “impossible” to break through the grieving multitudes to bury Khomeini before dusk.

The funeral was recognized by Guinness World Records as the largest percentage of a population to attend a funeral, drawing an estimated 10.2 million people — about one-sixth of Iran’s population at the time.

Khomeini died of a heart attack on June 3, 1989, just 11 days after intestinal surgery, without having resolved the question of who would succeed him. He left a 29-page “political testament,” excerpts of which were read over Tehran radio, though they made no reference to how Iran should be governed after his death.

In the immediate aftermath, President Ali Khamenei, then 49, was appointed caretaker leader. A presidential election and referendum on constitutional reforms were scheduled for Aug. 18. Khamenei’s swift appointment was designed mainly to fill the vacuum amid political turmoil that had prevailed since Khomeini launched his resurgence of Islamic fundamentalism in February with a call for the death of British novelist Salman Rushdie.

In the absence of a single personality who could match Khomeini’s religious and political authority, it seemed likely that Iran would be ruled by a collective leadership. Khamenei endorsed the presidential candidacy of Parliament Speaker Hashemi Rafsanjani, then 55, a political ally and the only declared candidate.

From exile in France, former Iranian President Abolhassen Bani-Sadr offered a grim assessment: “Imagine a church that cannot find a pope. It is exactly the same, like a dynasty that cannot find a king. … It will not last.”

Now, 37 years later, Iran once again finds itself preparing for a monumental funeral — this time for Khamenei, the very man who was elevated to fill the void left by Khomeini’s death. Whether the coming days will mirror the chaos of 1989 remains to be seen, but the images of that sweltering June day — of a nation grieving so intensely that it lost control of its own farewell — remain etched in the country’s collective memory.