The regime-changing wave of protests started after Tunisians successfully ousted their president in a popular uprising.
Egypt's then-nameless revolutionaries had created a Facebook "event" for January 25, like those for birthday parties or dinner gatherings.
They gave it an ominous name:
"The Day of the Revolution Against Torture, Poverty, Corruption and Unemployment."
More than 80,000 people clicked "yes" on the invite, indicating they would attend, according to Ahmed Saleh, one of the five administrators of the Facebook page.
Mahmoud Salem, 29, one of Egypt's most prominent bloggers, saw the Facebook event come across his Twitter feed. At first, he didn't believe it was real.
"Who does a Facebook event for a revolution, you know?"
Salem RSVP'd a skeptical "maybe" on the Facebook page. And, like many others, including the event's organizers, he showed up in the streets of Cairo that Tuesday, doubtful that the event would amount to much.
Soon, though, he found himself in a throng of thousands shoving against police barricades "like a bowling ball," trying to create a way for protesters to get through.
In that moment, for him, a digital movement became real.
More here: The faces of Egypt's 'Revolution 2.0' -