The Black Lives Matter movement has reportedly planned a nationwide set of demonstrations on Friday afternoon and evening, calling it their “Day of Rage” — though it was originally uncertain whether the protests were real or just propaganda by the Anonymous hacking collective.

The term “Day of Rage” described radical protests in the late 1960s — and, more recently, was used by Islamists during the Arab Spring to motivate protests against secular autocracies in the Middle East.

During the Arab Spring, so-called “Days of Rage” happened frequently on Fridays, because that is the day of the week when Muslims traditionally gather at mosques for midday prayers. In the repressive political environment of many Arab regimes, where there is no freedom of assembly, religious prayers were the only opportunity to bring large groups of people together.

The tradition of using mosque services to spark mass protests is one that many regimes had used themselves — though the targets of state-instigated “rage” had traditionally been the U.S., Israel, and rival Arab regimes, not governments themselves.

Liberal opponents of Arab regimes, who were among the early leaders of the Arab Spring, were quickly overtaken by their Islamist rivals in the opposition, especially the Muslim Brotherhood, which was elected to power in 2012 before being ousted in a 2013 coup.

SFist.com notes that the term “Day of Rage” was first used in connection with protests against the death of Michael Brown at police hands in 2014 (the event that originally inspired “Black Lives Matter,” though much of what activists believed about it at the time turned out to be untrue):

Several days ago, word went out via a series of emails and posts in conservative media that Anonymous and/or Black Lives Matter was planning “Day of Rage” protests today. The Dallas County Sheriff’s Department is said to be bracing for this, and the Defense Department even sent out a warning to its employees to avoid the DC rally location, which is outside the White House, “for your personal safety.” But as Snopes points out, the email that went out with the locations in 37 cities and using the term “Day of Rage” are nearly identical to a message that circulated in August 2014, in the wake of the shooting of Michael Brown in Ferguson.

Whether the protests are authorized or not, some people are clearly taking them seriously. In Cleveland, for example, Black Lives Matter began a “Day of Rage” protest on Friday evening, near the site of the Republican National Convention.

Joel B. Pollak is Senior Editor-at-Large at Breitbart News. His new book, See No Evil: 19 Hard Truths the Left Can’t Handle, will be published by Regnery on July 25 and is available for pre-order through Amazon. Follow him on Twitter at @joelpollak.