On the snowy streets of Moscow, many protesters said they were ready to go to jail.
“I’m prepared to be arrested, I know what to do,” said Ruslan Katayev, 22, a social worker, in an interview a minute or so before he was in fact arrested. He had said he had a lawyer’s phone number.
He had come out, he said, because “the main demand was not fulfilled: Free Navalny from illegal arrest.”
Dozens of people could be seen being detained at Clean Ponds, a boulevard park in the city center. Nikolai Babikov, 31, a computer systems analyst, gazed apprehensively at the riot police and at the chunky gray police vans that hold detainees, parked and ready nearby.
“Arrest would be unpleasant,” he said.
He said he had turned out to protest repression.
“The bolts are tightening,” he said. “Freedom is being eliminated and bit by bit we are becoming the Soviet Union again.”
As the day began, a steady stream of mostly young people walked along the Garden Ring, the broad circular thoroughfare surrounding the city center, toward the meeting point announced by Mr. Navalny’s team. Some tried taking side streets and found them also flooded with police officers.
Older people joined the protest as well. One of them, Lyudmila Mikhailovna, an 83-year-old retired pediatric doctor who declined to give her last name, said she was no great fan of Mr. Navalny. But she had watched his video about the palace he said was built for President Vladimir V. Putin and decided to join the protest because “I am for honesty, nothing else.”