The Four Hundred and Four is a legend among the Vulcan people, telling of followers of Surak during the time of the Sundering. These followers would preach logic and peace to their war-like kin, leading to their murders. However, despite the numerous deaths, another would take the fallen Vulcan's place.
Millenia later, the legend would be remembered as those who gave their lives in the pursit of peace. Many Vulcan masters are known to have memorized the death speeches of each of the Four Hundred and Four who were slain to bring about Surak's teachings. (Last Unicorn RPG module: The Way of Kolinahr: The Vulcans)