Iran's rulers confront their most serious challenge since their own 1979 revolution.
They're now countering on an unprecedented scale - a ferocious security crackdown and near total internet shutdown has been unleashed on a scale unseen in previous crises.
Many of the streets once engulfed by a roar of anger against the regime are now starting to go silent.
"On Friday it was extremely crowded - the crowd was unbelievable - and there was a lot of shooting. Then Saturday night it became much, much quieter," a resident of Tehran told BBC Persian.
"You would have to have a death wish to go out now," one Iranian journalist reflected.
