Too angry to be cowed, they poured into the street, fed up with their country’s wide-reaching corruption and a government unwilling, or unable, to stop it. Police responded with barricades, tear gas and mass arrests in cities across Russia.

By Sunday evening, riot police in body armor and helmets had hauled in more than 700 demonstrators in central Moscow, as the crowd, numbering in the tens of thousands, cheered, whistled and chanted, “Shame! Shame!” . . . One of the first detained in Moscow was the chief architect of the rallies, Alexei Navalny, who called on people to protest in the wake of his allegations that Prime Minister Dmitry Medvedev has amassed vineyards, luxury yachts and lavish mansions worth more than $1 billion.