Ayatollah Khomeini referred to Karbala and martyrdom many times in his speeches, most notably in the speech given on the eve of the Shah's departure from Iran "[Husayn] taught us that if a tyrant rules despotically over the Muslims in any age, we must rise up against him."[20] Khomeini labeled the Shah as "the Yazid of our time,"[21] referring to the caliph of Husayn's time whose soldiers were responsible for the Karbala massacre. Popular slogans also reflected the importance of symbols of martyrdom, such as the slogan often seen on banners: "every land is Karbala, every month is Muharram, every day is Ashura."[22] The revolutionaries therefore considered those who died at the hands of the Shah's secret police to be martyrs, especially those killed during the Black Friday Massacre (link), a clash between government troops and peaceful protestors that led to the deaths of around 100 people. The willingness of the revolutionaries to die for their cause in the name of martyrdom was a powerful tool in overthrowing the Shah.