OSLO, Norway - They gathered by the tens of thousands, aiming to face down terror with the power of music.

Inspired by a Facebook-organized protest, Norwegians flocked to public squares across the country Thursday, ignored the drenching rain and lifted their voices in song.

Their target: far-right fanatic Anders Behring Breivik, now on trial for a bomb-and-shooting rampage that killed 77 people. Their weapon: a children's tune that he claims has been used to brainwash the country's youth into supporting immigration.

Defiant sing-alongs of "Children of the Rainbow" were staged in Oslo and other major Norwegian cities, while in court survivors of Breivik's attacks gave tearful testimony in the ninth day of his trial.

In downtown Oslo alone, about 40,000 people chimed in as artist Lillebjoern Nilsen played the song - a Norwegian version of American folk singer Pete Seeger's "My Rainbow Race."

They sang the Norwegian lyrics:

"A sky full of stars, blue sea as far as you can see

An earth where flowers grow, can you wish for more?

Together shall we live, every sister, brother

Young children of the rainbow, a fertile land."

In testimony last week, Breivik mentioned the tune as an example of how he believes "cultural Marxists" have infiltrated Norwegian schools and weakened its society.

Later, the crowd marched to the Oslo courthouse, where they laid a carpet of red and white roses.

Reached at home in Beacon, N.Y., Seeger, 92, told the Associated Press he had heard about the mass gathering from Nilsen, who called him Thursday morning. "I said, 'Oh that's wonderful,' " Seeger said. "One of the greatest honors a songwriter could have is to have a song of theirs sung in another country."

Breivik has admitted setting off a bomb on July 22 outside the government headquarters that killed eight people, and then going on a shooting rampage at the Labor Party's annual youth camp on Utoya island, killing 69 others, mostly teenagers.

Shocked by Breivik's lack of remorse for his massacre, Norwegians by and large have decided the best way to confront him is by demonstrating their commitment to everything he loathes. Instead of raging against the gunman, they have manifested their support for tolerance and democracy.

Eskil Pedersen, the head of the Labor Party's youth wing, told the umbrella-decked crowd in Oslo that Thursday's song held special significance for his group. "We aren't here because of him, but because of each other," Pedersen said.

Breivik's lawyer, Geir Lippestad, said his client was aware of the protests.

In court Thursday, people who survived Breivik's car bomb gave emotional testimony as he sat expressionlessly.

Anne Helene Lund, 24, was just 23 feet from the explosion. She was in a coma for a month and woke without memory, unable to even remember the names of her parents. "I studied political science for three years, now I have to relearn social studies at the junior high school level," she told the court.