What began as a solemn religious gathering in the heart of the Iranian capital erupted into one of the largest anti-Israel demonstrations in recent memory, as millions of Iranians filled the 10-kilometer stretch between Imam Hossein and Azadi squares on Saturday evening.

The major public event named “Iran; Zulfiqar of Ali” began in Tehran simultaneously with similar events held across the country. It was originally organized to commemorate a major Shia religious holiday, turned into a thunderous chorus of defiance and fury, as the crowd reacted to Israel’s recent missile attacks on Iranian soil—an escalation that has left dozens of senior military figures martyred and pushed the region toward the brink of full-scale war.